If you are a master student, you can just go ahead and register for class once you have your mysjsu account setup. Don't worry about the tuition. You won't be asking to pay the fees after your appointed registeration slot. You can always add and drop class within the first week after school started. If you want to drop or add after your assigned registration time, you will need to get an add code from the professor which might not be easy to come by depending on the department and the professor. Anyway, just go ahead and register any class you feel like and you can drop it later. Better early than late