Sex is an act preformed emotionally and physically sex organs play an important role.  Here is the description of sex organs:

Males Organs: The sex  organs  of a male are quite  complicated  form of a reproductive  system.  They produce  semen, store it and release into the woman's vagina at the time of ejaculation.  Procreation, therefore, is the result of the union of the sperm cell and the ovum.

Tests: The male  organs comprise of the two testes  of testicles hung side by side in a  sac  called the scrotum, behind the penis  in its relaxed state.  The testes are oval in shape and about an inch  long and  inch wide, have two different functions.  These are made  up of a series  of lobes composed of minute  tubules in which the sperm cells  the spermatozoa are formed and liberated.  The internal secretion of sex hormones which  create sex impulses and cause the essential male characteristics in the individual and play its role with the other secretory glands  in he body in sustaining the normal functioning of the body, are achieved by it.  In case this function is impaired before puberty,   the development of the individual becomes seriously altered in form, temperament and impulses.  Since  it is  directly absorbed into the blood, these secretions are termed  as internal  secretions.
            In the seminal discharge  the male sperms formed in the testes are  the vital elements because  these sperms have the power  of fertilizing the egg of the woman   to conceive a  new life.  These highly vitalized  cells consist of a head, neck and long tail.  It is in this head  that  the nucleus  is contained  which transmit the hereditary characteristics of the individual.   Having the power of  independent motion these  sperms propel themselves in the liquid  secretion in which it floats, it requires an hour or more for the sperm to reach  the cavity of the uterus and a few  hours to gain the oviduct or the  tube   where in fertilizes an ovum (egg).  When the released female egg  encounters one male  sperm it penetrates the cell wall of the egg  in an complex series of rearrangement of both  cells, known as fertilization.  Though, in single male organism  about 200 to 500 millions sperms are discharged,  only one is able to  reach the walls of the cell.  The remaining cells  are cast out along with the  other residues  of the physiological process.  The spermatozoa are being slowly  formed and released in the testicles all the time.

Epididymis and Vas Deference: Each of the cluster  of convoluted tubes in the lobes of the  testes in which the sperm cells are formed merges into a  single tube and the resulting mass of   tubes  in turn forms a complex network which constitutes a large annexes to the  body of the testes.  It is known as epididymis.  The network  of the tubes of epididymis unite in  turn to form the seminal duct  or vas deferens.  From the  epididymis  each seminal duct  passes upwards  in the scrotal sac and enters  the pelvis  cavity where it continues  its upward  course, then curves forward  and  downward  to enter the  urethra which conducts the urine from   the bladder.

Seminal vesicles: The vas in number, issuing  from each testes takes a round  of the bladder and then  empty into the seminal vesicles.   These vesicles are two  small pouches, situated  just behind the urinary bladder.   The function of seminal vesicles is to  store the semen and secrete a gelatinous substance  which  by mixing   with the sperm thickens the semen and  increases  its volume.  The secretion,  the sperm thickens the semen  and increases  its volume.  The secretion  also  provides   nourishment and strength to sperms.
            Since  these testes and seminal vesicles are always secreting and manufacturing  semen,  sometimes  the vesicles are filled to capacity and the nature empties them in the form of nocturnal emissions as is in the process orgasm.  The phenomenon is usually accompanied by erotic dreams and pleasurable sex feelings of an orgasm.
            It is a  mistaken belief  of old  theories  that nocturnal emission or wet  dreams are a sign of weakness.  These are natural, harmless occurrence to be expected in most normal men., particularly between  the ages of fourteen  and thirty -five.  There is nothing to worry about.   Untold  mental torture   and unnecessary  expense   has been caused  to millions of men through  the misrepresentation of quacks and fear of men  in these matters.
            Seminal emissions vary greatly in frequency of occurrence  between different  men and  in the  same  man at different times.   Within the normal  the frequency  may range between once a month  to several times a week.  Many factors, physical,  mental and temperamental - are responsible for it.  there are  some young men who rarely or never experience nocturnal emissions.  Though the occurrence   of emissions are natural, their absence  does not necessarily  indicate  any abnormality.  It is quite  possible in their case that the contents  naturally ooze out in the ducts aided by bowel movements, to be thrown out with  the urine from the bladder.
            Nocturnal emissions generally occur when a man sleeps on his back.  The reason being that in this position  the weight of the partly filled or full bladder  resting upon the  vesicles increases the irritation to set of the  reflexes  ejaculating  semen.  To avoid  this, heavy  food should not be taken before going to bed  and constipation should not be allowed.

Prostate Gland: It is shaped  like a horse chest nut.  Surrounding the neck of the bladder  and the junction  of the urinary and spermatic ducts, into which juncture the prostate empties its contents through some thirty outlets.  The prostate  secretion is also added to  the semen before  it is ejaculated  in the vagina.  Thus semen  is a combined product   of all these glands.  Each  of these  glands imparts to the semen its many peculiar characteristics.  The prostate is also a sexual gland, which  is situated   below  the urinary bladder.  During  coital climax, the prostate  contracts  and mixes  its own secretion  in the semen.  To sustain  sexual vigor and  strength, it is considered necessary  that the  prostate functions properly.  The prostate secretes a thin milky, alkaline fluid, function of which is similar to the products of the vesicles.  The  alkalinity serves to protect the spermatozoa against acidity damages the vitality of the sperm cells.

Urethra: A small  duct   called urethra runs though  the center of the penis down to its glands from the urinary bladder.  This duct serves the double  purpose it empties the urine from the bladder and ejaculates  the semen  from the seminal vesicles.  Thus urethra is connected with both  the systems of seminal discharge and urine  elimination.   The urethra in penis  discharges both semen and urine  but sex  mechanism of male body  is such   that both  the actions cannot take place together.  During seminal discharge special  valve  automatically shuts off the urine.

Penis: A child's penis is small which  grows long with the other  organ of the body after  the onset of puberty.  Penis through which  the bladder is emptied and the  sperm is discharged  during  intercourse, is normally  three to four  inches  long  and in normal flaccid state  about one and a quarter to two  inches in diameter.  When a man  is sexually aroused his penis grows   erect and  organ measures about one and a half inches   in diameter and five and half  to sex and a half   inches in length  along its upper side.  It is  made up in part of spongy tissue which becomes gorged with blood, making the organ hard and rigid.   In excited state it stands  out an angle from the body to confirm  in general to the normal  vagina  angle  of the woman.  The erection is essential in order to achieve the penetration of the vagina.  In response to mechanical or psychic stimulation,  the erection is achieved through a nervous mechanism which causes a rush  of blood  into  the organ and at the  same  time greatly restricts  its flow thus, causing rigid  distention of the penis, Like the size, the shape also varies   from man to man.  Penis is the male copulating organ which conducts the semen into  vagina.  There is no correlation  between   the size of the penis and  a man's sexual  strength and capacity.   The erect size also does not  make much difference because  vagina has  such an elastic cavity to accommodate any size of penis.  The most  sensitive nerve ending in a vagina is the clitoris which  can always  be reached by any penis howsoever  it be small.

Glans Penis: The foremost end of the penis round like  a knob  is called glans penis.  It is slight thicker than the rest of the shaft.  In the  flaccid state of the  penis the head or glans penis is partly or wholly by a loose layer of the skin, in the uncircumcised, called the prepuce of foreskin.  This is retract for the purpose of cleaning and it becomes  natural retracted after entry in coitus.  The surface   of the foreskin is somewhat mucus owning to the glans  which secrete a substance called smegma.  It is  an irrigating secretion and should  be regularly cleaned, otherwise it makes the forepart of the  penis becomes cheesy in appearance by breeding  germs.  It should  be daily washed with soap.  The glans  penis has the most  sensitive nerve endings.   A slight  soft touch  is enough to excite  a man and to make the penis erect.   It is mainly the glans penis on which  a little  rubbing whether  by hand or by vaginal contact  sends the sex  waves in the entire body, culminating in orgasm or ejaculation.

Erection and Ejaculation: As also  referred to earlier, the effect  of the sexual  arousal in man is physically manifest in the erection of the penis.  A direct and gently stimulation of the penis almost always causes  erection.  This is   borne  out of reflex action and may occur in sleep.  Erection may be  caused without any rubbing of the penis, just by erotic thoughts  or dreams it goes  erect.   In the early morning it may be  aroused  because of the urge  to  urinate.  Most such erections terminate without  any discharge.
            Ejaculation is the culmination of sexual   stimulation in man.  Having entered the vagina, the most sensitive nerve endings of which the penis is made up,  become tense and excited  on account of the friction against  the walls of vagina, the cozy  heat  it may experience  further   fanned by the  secretion of the fluid in the vagina.  To and  from movements of the penis add on the  arousal.  The tension  gets higher  and higher till it reaches the climax  and the release  of the  seminal fluids is known as  ejaculation.  The basic  difference between the sex mechanism of the man and the woman is, in man the climax and  ejaculation or orgasm take place simultaneously while  in women these are two different  states.   At the  time of the climaxic height  orgasm the seminal discharge takes the places through the penis  in a number of spurts.  The number   of spurts varies  from 4 to 20  just  as the  first menses indicates the onset  of puberty in  a girl, the first  ejaculation marks  the boy's entrance  into adolescence.

Female organs: The female organs are more complicated  because  they are  confined in the body ad not  openly visible.  Because of the apparent  invisibility most of the girls are unaware about their  internal sex organs.  Hence, it is all the  more   necessary that full knowledge about  the female  organs structure and their function be discussed  in full details.

Vulva: The two visibly fleshy  folds, covered with hair are the outer lips or labia majora.  When  parted they reveal two smaller  or inner  lips of labia.  The insides  of the inner labia are covered with mucous membrane.  The inner  lips or labia  are  one of the several sexual sensation centers.  In sexual inter course these  labia  remain constantly massaged by the rubbing of penis.  In some women the inner  lips protrude somewhat.  The inner lips meet their   upper  ends which when  separated look like the form  of wish  bone of a hen.

Clitoris: The principle of the sex feeling, the clitoris is situated just above the junction of the inner  lips.  The clitoris looks like a mini penis having erectile tissue and a head and foreskin similar to the penis of the man.  It is covered from above by a  hood of skin.  The clitoris  is made up of highly sensitive nerves  which respond  very well to sexual stimulation.  It is form the is center that the sexual feeling  begins  and permeates in the entire body through  vulva and vagina.  When erect the clitoris looks like the size of or shape of small bean.  About an inch below the clitoris a small opening of the tube   called urethra.  Its duct conducts the urine  from the bladder.  The urethra  has only the urinary function and no  sexual function.
            The mucous membrane above the clitoris, like the penis of a man, is covered with glands  which secrete  smegma.  Owing to the  structure, cleanliness in the woman is somewhat  more difficult than it is in the man.
            It is not  hygienically necessary to keep it  clean but also  for this reason that it emits smell which tend to  inhibit  sexual desire in the  man.

Hymen: Just below the  urinary  passage is the entrance   to vagina.  In the normal virgin girl this opening remains partially close by a thin membrane  called the hymen.  Though it appears in different shapes but normally it looks like a crescent in shape  appearing the forward extension  of the  black walls  of the vagina.  In many  cases during the first  intercourse when the hymen  is ruptured there may be  slight  bleeding  and pain.  But this  should not cause any alarm.  It is a false notion which the orthodox still maintain that the  hymen is the symbol of virginity.  A nicked or stretched or tattered hymen does not mean  that the  body has been penetrated into.  It could be ruptured on account of many a jerks or falls that a young girl might  have experienced.  Many  girls may not have much of it or others may lose   it in doing  some kind of  vigorous job.  Sometimes  the insertion of a finger into the vagina  may prove too hard for any hymen.  Occasionally a hymen  is so tough that it remains intact even after several sessions of sexual intercourses.   It all depends on the kind of  hymen a girl is born with.
            Generally during the first  coitus, the  penis  tear it till hardly a few shreds mark it former presence.  At times in certain cases it was found to be so flexible that instead of breaking into pieces by the penile thrust, it  merely bends and allows the penis to glide over it.  It may  in certain cases  remain there even  after delivering a child.  In some cases the surgeon's  aid is obtained to slit open the membrane.  But the bleeding  and discomfort, when they occur  are not of sufficient consequence to warrant fear on the part of woman.
            This is psychologically  important because  this fear  powerfully inhibits her sexual  responses and  the function  of the lubricating glands, leaving the parts dry.  This increase the probability of discomfort  and bleeding and diminishes the possibility of experiencing   any sex pleasure   at the first  coitus.

Vagina: It is  tube or canal extending from vulva to the neck of the uterus.  It is three  and half to 4 inches in length in its normal relaxed position.   It is here that the penis in intercourse is sheathed with its elastic  walls.  It receives the   seminal discharge and   allows the sperm to travel  forward towards the womb in search  of the ovum.  It is through this tube that a child passes to the outside world  during  pregnancy.  The  vagina  and its outlet becomes capable to great expansion, permitting the passage of the child from the womb without   injury in may cases.  In mot instances, however  more or less laceration of the muscular  structure controlling the opening and of the  vagina  itself occurs.  It should be   vitally  important that such tears receive prompt surgical attention.  The use and control  of the muscles about the  vaginal  opening of the entire pelvic floor are  necessary to woman's most effect participation in coitus.  The relaxed condition and the loss   of muscular control which results from  the failure to repair perineal and vaginal tears may result in greatly diminishing sexual satisfaction in coitus for both partners and a render it  impossible for the women to achieve orgasm at all.  The flexible  walls of the vagina are lined moist and clean.  It  has a great   relaxing and contracting power.  It is because  of this reason that the vagina, besides being made up of flexible  walls, is able to accommodate must larger penis not  with standing  its small cavity.

Womb or Uterus: It is  pear shaped organ   of heavy muscular walls.  The virgin  uterus measures about  two inches wide.   Its elastic muscles expand considerably during pregnancy with the growth  of the baby.  Its upper part is connected with ovaries by two ducts  called fallopian tubes.  The organ is supported in the pelvis by strong ligaments, its position is at right  angles  to the vagina.  The upper, heavy  end being directed  forward  towards the front of the pelvis.  The small   end  opens into the vagina  and closes its upper end.  After childbirth  the organ gradually retracts to its normal size.  The organ  has powerful  muscles to help push  the baby  out through the vagina.  During  pregnancy, the uterus retains   and supplies nourishment to the growing baby till the delivery.

Fallopian tunes and ovaries: The upper end of the uterus as referred  earlier are joined by the  fallopian tubes, each about  five half inches long, which extend  right and  left  to the ovaries.  The function  of the fallopian tune is to conduct  ovum from the ovaries to the uterus.  This is  achieved through contractile action  of the tubes finger like  fringes called fimbria.  The sweeping  motion of fimbria is in one direction,  which  help the egg cells in moving towards uterus.  In most cases, the  fertilization of an egg cell or ovum takes  place during  its journey through   the tune is  called   ovulation.  The fertilized egg is then moved down the tube  towards the womb.
            The  ovaries  can be compared  likened to the testes of the  male.  They produce  the female reproductive cells, the ova (eggs) and  internal  secretions.  Situated  at the outer  ends of the  tubes, one on each side of the uterus, an ovary is about the size and  shape of  a large almond in the  shell.  Though they are comparable to the testes in their  function, the hormone function of the  ovaries  is apparently more  complex than that of the testes of the male.  In addition to the internal  secretion which  governs development of the  specific  female character and help  to sustain the normal functioning of the individual  as an organism, the  ovaries elaborate other chemical sustain the normal  functioning of the individuals as an organism, the ovaries elaborate other chemical substances which control the reproductive  functions.  If the ovaries are removed before  puberty  the development of the individual  gets drastically altered.  Even  after marriage, if  ovary is removed   for any reason,  there could be certain changes felt   physically and mentally.
            When a  girl is born, here ovaries already contain these egg cells or ova in tens  of thousand.  But then  these are not  mature.  With the onset of puberty the ovaries  start their work of maturing ovum.  During  the life  time of woman about 400-500 of egg  cells mature.   From the time of puberty till menopause , every month a mature egg is produced by one of the ovaries.  The mature egg cell passes through  the fallopian tube  towards the uterus.  If an egg is fertilized it starts growing before it enters the velvety lined uterus which nourishes the egg will.  If the  egg is not  fertilized it remains alive for about 20-44 hours  after entering  the tube and then it disintegrates and gets absorbed  into the body.   In that case  soft and velvety  lining of  uterus is not required,  the blood  and the blood vessels forming  the protective lining are cast out through vagina.

Menstruation: When the egg cell is not fertilized, the monthly  preparation  by the womb to received  a fertilized egg cell gone a waste and the debris is cast out the whole process is known as menstruation.  Menstruation  generally continues for three to five days but even longer in few cases.  While  it is a normal physiological function, not to be regarded as a 'sickness' or being 'unwell' in several cases  the general   let down and the readjustments of entire organism do involve  nervous tensions and in many cases a variety of aches  and pains  for which  due allowance is to be  made in the social  and personal  circle of the individual.
            It should be  clearly understood  that a girl or woman  during the periods, should not be considered an 'untouchable'.  As a matter of  fact, the underlying reason of this  belief was sympathetic- that in a period of menstruation, a girl or a lady might feel weak so she should be  given full  rest - which has been mistakenly converted into a hygienic  one.   But now-a-days not educated girl or  woman  adhere to these obscurantic norms and treat the period days like any  other day in their life.  May be, because of  better facilities to contain this blood into the  sanitary napkins, the  modern woman does not make it a show of it.  It is not physically but emotionally a woman might feel disturbed during this period, for which she should be shown due consideration.

Breasts: Though the breasts do not strictly come under the category of the organs we are discussing, they are being induced because of their special significance in manifestation of the sexual arousal of a woman.  Especially their breasts' nipples signify as one of the most erogenous zones on woman's body.  Squeezing, sucking, touching, caressing of the breasts, particularly the nipples give rise to strong and most favorable sexual desires.  The sexologist says that in the initial stages of married life a woman derives more pleasure from any such stimulation of her breast than the actual coitus.  Nipples, like clitoris have erectile    tissues and very sensitive nerve endings.  The tissues become firm and   erect during erotic stimulation.  It is for this reason that breasts or mammary glands are two very important sexual organs, whose development is dependent on the secretion of certain hormones of the female sex.  Though, the breasts have their primary function in feeding a few born child there importance as an erotic and sensitive   zone permeating with desire to make has great   significant in sexual relationship.  Although   their sizes vary from puberty to maturity and they grow large during pregnancy .  The sexual undertone of this organ has influenced the loving onlookers most.  An ideally formed breast has always been the most beautiful female symbol or characteristic