The difference in a law and a theory is that a law can be tested with experiments, but a theory can not or has not been tested. Evolution as a theory can not be tested like the law of gravity. Evolution is an ancient idea that life began due to a slow process of simple things automatically becoming more complex. Evolution is broken down into three different main categories. The first is microevolution.
Microevolution is the change within a species over time.
Microevolution is not controversial. It is the basic idea that a species has variety. Macroevolution is controversial. The last is the philosophy of evolution. This, like all other philosophies, is controversial.