That’s a really complex and profound question! The simplest answer is that they come from our observations about the universe. Over the course of thousands and thousands of experiments, scientists have seen that there are regularities in the way certain things work. They refer to these regularities as laws, and that allows lots of different theories to be developed that use the laws as their basis. As to why the laws of physics are the way that they are, I guess no one really knows. Or at least, I don’t!