Class is Full? What do do?
Sometimes (every time if you’re a CS major), a class you want may already be full when you try to enroll in it (upperclassmen have already pre-enrolled in classes!). Freshman get last pick for classes. However, classes tend to have a lot of movement during the first week of school, and classes will fill up/open up. Keep a close eye on classes you didn’t manage to get in, and use a course tracker to notify yourself when a class opens up.
If you really need to take a specific class during a specific semester, talk to the professor/TAs and attend the first class. They may be able to work something out.