When you create an account on Classroom, this automatically creates a folder on your My Drive called Classroom.
When you create a class it creates a folder within Classroom with the class name. Click on the folder icon at the bottom of the class card on the Classes page.
When you create assignments, these are stored in folders with the class folder. It does all this file and folder admin for you. Plus, the materials are automatically shared with your students, so you don't need to worry about that either.
You can add files and folders to this folder, for example, for materials that you're going to use in the course.