Just because we evolved from a common ancestor with apes doesn't mean that long ago, there was a creature who was born with ape-like qualities, who lived a really long time and as he grew older became more and more like a human. It was a gradual process that took many, many generations.
Long ago, there was a population of creatures which were a common ancestor to humans and apes. That population, for some reason, broke up, with one part moving into an environment which made ape-like creatures more likely to survive, while the other group moved into an environment which favored human-like creatures. The ones with the genes which best suited their environment were more likely to live to an age at which they could have children. All the others died before they could reproduce. The ones that reproduced passed on their genes to their children, so eventually, since apes and humans come from different environments, they adapted in different ways.
The main reason we seem to have stopped evolving is because one of the biggest factors in evolution is natural selection. Now that there are over 6 billion people in the world, and little to no competition from other animals, not much natural selection goes on, so our species doesn't change very much.
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