When two parents mate, the sperm enters through Vagina and fuses with Ovum in Fallopian tubule. This is called "Fertilisation". The fertilized egg (Zygote) moves towards Uterus and implants to wall of Uterus and develops into Foetus (Baby). The total development from Zygote to Foetus takes more time in mammals this is called "Gesitation" period. Foetus obtain nourishment from mother through structure called "Placenta" and waste material are released to mothers blood through Placenta, at the end of Gesitation period, muscles of Uterus contracts so that foetus come out through Vagina.

Note:- Gesitation period in Human being is 9 months.