Good morning, @Rye ...
Often times, a school has processes in place where you would register for classes via their Student Information System, and then once you register for classes there, your information is sent automatically into the Canvas LMS (Learning Management System). Your school may have something similar in place already. Other times, depending on the school, you might be manually added to a course by your instructor. It really depends on the school, so I'd encourage you to reach out to your school's Registration department or even someone from their Online Learning / eLearning / Distance Learning department to see how things are handled.
I hope this will help in some way. Good luck as you have these conversations!
