About six million years ago, the earliest people evolved from earlier primates in East Africa. People seem to have evolved in order to take advantage of new grasslands that were taking over from the jungle in Africa beginning about eight million years ago as the Earth cooled down. Very soon, these people began to walk on two feet, so they could run faster in the grasslands to get away from danger or hunt animals, and their arms became weaker and shorter, because they didn't need to swing from trees anymore. These first people were still pretty hairy, like monkeys, and had small brains. Possibly they continued to have babies with chimpanzees sometimes for another million years. They probably ate mostly roots like yams, nuts, fruit, insects, meat, and fish and shellfish.
By about two million years ago, modern humans were beginning to evolve. They lost their body hair and developed black skin to protect them from the sun. They began to have bigger brains. Their tongues and throats evolved so that they could talk. About one million years ago, people figured out how to make fires to cook their food and keep warm.
About 60,000 BC, when the first humans began to live further north, in Europe and Asia, to keep warm they had to re-evolve some of the body hair they had lost in Africa. They also re-evolved the pink skin of other primates, so that they could absorb more Vitamin D from the smaller amount of sunlight they had. When humans first began to keep cattle and sheep, about 6000 BC, some of them evolved the ability to digest milk. That's why some people can digest milk and others can't. People are still evolving today, though it happens so slowly that it's hard for us to see.
To find out more about early humans, check out these books from Amazon.com or from your library: