When a man becomes mature and independent to get married, he plays important role in making of a baby.

When woman becomes mature, an egg is produced in one of the ovaries of a woman which is released each month to be picked and preserved in the Fallopian tube for 2 to 3 days.

During this time, if any sperm from the semen deposited by the man reaches the egg, the fertilization can take place.

Process of Reproduction i.e. Formation of Baby is results of union of 'Sperm' produced in the man's body with that of 'Egg' released in woman's body.

In natural course this union occurs through Sexual Intercourse

Sexual Intercourse occurs when a man inserts his erect penis through the special opening in the woman’s groin region called vagina.

To and fro movements of Penis into the Vagina followed by series of muscular contractions, result in ejaculation of semen from the penis in spurts, into the space in the vaginal canal.

This Semen contains Sperms which enter the woman’s womb. These sperm travel through the womb (Uterus) and through the Fallopian Tube to reach the Egg.

Only one Sperm unites with the Egg to complete the process of Fertilization. Remaining sperm get disintegrated and dissolve the cavity of Uterus and Fallopian Tube harmlessly.

Fertilized egg then travels through the Fallopian Tube into the Uterine Cavity (Womb) and gets embedded in its lining.

This embedded Fertilized Egg then forms a baby in 36 to 40 weeks' time.

Every month one of the ovaries of a woman produces a mature egg which remains in the Fallopian tube for 2-3 days where it is able to get fertilized.  

Once the semen is deposited  into the vaginal canal by sexual intercourse, the sperms  move on their own into the uterus through cervix and through Fallopian tube try to reach the matured egg.

The egg once fertilized, seals off the entry to other sperms.

This fertilized cell then keeps doubling to make the multicellular structure (called morula) which travels to the inner space of the uterus and gets attached to its special lining called endometrium till it develops into a baby. 

The strong muscular walls of the uterus expand to give space and protection to the growing baby.

In about nine month’s time, when the baby is ready to take birth, it comes out of the uterus due to contraction of its musculature and expansion of cervical and vaginal opening.

The Baby then gets delivered through passage of Vagina along with the lining of the Uterus which was holding the baby during its development. 

• Insertion of penis and deposits of sperms into vagina can lead to pregnancy.
  
  
• Pregnancy is possible even on first intercourse and even if menstruation has not started or not regularly started. It may have coincided with very first ovulation
  
  
• The spilling of semen on outer part of vagina can lead to pregnancy
  
  
• Pregnancy is possible even without orgasm.  Mere insertion of penis and deposits of sperms into vagina can lead to pregnancy
  
  
• Oral Sex can never lead to pregnancy
  
  
• Anal Sex also can never lead to pregnancy.  But, spilling of semen over the vulva i.e. entrance of vagina, can lead to pregnancy
  
  
• Presence of tampons does not prevent passage of sperms, although it allows lesser space in vagina for the erect penis
  
  
• Pregnancy cannot be avoided by jumping, skipping, hot bath, or alcohol consumption
  
  
• Pregnancy takes place only when the sperms enter the vagina and meet the ova in the fallopian tube
  
  
• Deposition of sperms in vagina is only possible by insertion of penis but sometimes even the spilling of semen on outer part of vagina can lead to pregnancy.  This is because of high motility of sperms and favourable conditions created by secretions around the vagina during the most fertile period of the cycle
  
  
• Position does not matter in preventing conception.  Sex even in standing position can lead to pregnancy because sperms can always swim upwards towards uterus and allowed entry into uterus.  Release of mature egg within a day or two after intercourse can always have increased probability of fertilization
  
  
• Since every drop of semen contains thousands of sperms having motility, i.e. ability to move on their own in any direction. In favourable condition these sperm may find their way inward and upward inside the uterus to fallopian tubes and lead to fertilization
  
  
• Pregnancy is also possible even by intercourse during menstruation (periods).  Even in normal circumstances it is likely that mature egg gets released from the ovary while a girl is menstruating so contraceptive is essential
  
  
• In case where suitable protection is not available it is better to avoid penetration and opt for alternatives for sexual gratification of each other and refrain from intercourse.