php oop - each class different file? import package? etc

I am used to working in languages such as C#/Java/Python where each class would have its own file, and for a class to see other classes, you would import the package containing those classes. How does this work in php? The documentation shows you how to create classes, but I don't understand how it all fits together in a php context. I know of the include statement, which just sticks the files together basically.