Sex, the art of reproduction.
So if you've read the two pages Female Puberty and Male Puberty you're probably thinking why do bodies need to change? How are babies really made? Well I can tell you now it wasn't the stork!
Babies are made by reproduction which involves something called sex. When a man and woman start kissing and hugging the man's penis gets excited and he has an erection. After some more kissing and hugging and a bit more hugging and kissing the man and woman get naked. Now this usually happens on a bed because the couple can lie down comfortably. Now once both the man and woman are sexually excited the man puts his penis inside the woman's vagina. Yes that's right inside. He pushes it in and out, massaging it, until him and the woman orgasm (a really intense pleasurable feeling). At the end the man will release his sperm into the woman's vagina and the sperm will swim up the vagina in the hopes to meet and egg and grow into a baby. But the circumstances are not always perfect for this to happen. To increase the chances of becoming pregnant the woman must be ovulating, this is when her egg is ready and in the right place to be fertilised by a sperm.
But people don't always want to have a baby when they have sex so there a thing called contraception that stop the egg and sperm meeting. You can read more about these in the contraceptives section.
Sex is a very enjoyable experience for both the man and the woman. Sex is enjoyable because if the couple enjoy it, it will increase the chances of them doing it again therefore becoming pregnant and continuing the human race, this is called an adaptation, but you'll learn more about that in science at school.