A theory is not a law. 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.