<p>Oh, it’s easy. You have a period of pre-registration where you pick up to six cources you’d like to take and list up to three choices for which section of the class you’d like. You state your preference for three or four. Then you’ll somehow be assigned three or four classes, though sometimes you’ll want four and only be placed into three. After that the add/drop period begins. This is all at the end of the previous quarter. During the add/drop period, you can change your mind about what you want to take as long as the sections are open. After classes start, people can try to get into courses that you can’t “add” online because they’re full. You get the professor to sign off on a “pink slip” letting you into the class, and you drop off the pink slip with the registrar. Professors stop letting new people into the class after the first week, if they let anyone additional in at all. You can drop a class anytime in the first three weeks. That’s another reason why it’s smart to sign up for four classes–so that you can drop one without worrying about adding another. Everyone adds and drops classes. It’s really common.</p>