The birds and the bees. The stork delivery the baby. At some age there comes a moment where everyone has to learn where babies come from. Let's face it: the human reproductive system is complicated. And that's probably the reason we use euphemisms.
Fertilization happens internally when a sperm and egg collide. They combine to form a zygote. The zygote travels into the uterus where it buries itself into the lining of the uterine wall. This process marks the beginning period of pregnancy. After this, the pregnancy continues for nine months as the fetus develops more and more.
In a female, the reproductive system has two jobs: produce an egg and protect a fertilized egg until birth. In a male, the reproductive system has one job: to make and deliver sperm. In addition to different reproductive organs, males and females also have differences in secondary sex characteristics. Secondary sex characteristics are things like body hair, Adam's apples, and facial hair.