It takes up to millions and millions of years for evolution to happen because a mutation will need to happen and the animal that has the mutation will have to have offspring with that mutation. Then over time that whole species will have to that have the mutation for evolution to happen.
Evolution is a change in species that starts with a mutation. Mutation can be good or bad, when it's good it can help the animal hide from predators. If it's bad the animal can possibly die or easy to see to predators.
Natural selection is a chooser between the winners and the losers instead of being random. Unlike natural selection mutation is random, mutation is a random fault in the genes. This video will give you more details about natural selection.
This is a video that gives evidence on evolution and some facts on how evolution starts.