The process of signing up for classes and getting approved is called registration. Photo registration Usually takes a few hours and is fairly simple. Just show up to your freshman orientation, listen to a few speakers, do a few tasks, meet with your adviser, and eventually select your classes.
The first step in beginning your college career, before registering for college classes, is to apply to schools. You will receive letters in the mail stating if you have been accepted or declined, and the reasons why. Whether you get declined or approved is based on how high your high school GPA is, your test scores, and the requirements of the college. Ivy League schools like Harvard University and Yale are obviously going to have much higher requirements than an average college. These school are incredibly hard to get accepted into and only the best students get in.
When going through the whole registration for college classes process, I would recommend taking a full schedule to start with, because you can always drop classes later on. Most colleges allow around a months time before you can no longer drop classes. This is great because you can go to a class several times, realize it's not going to be something you want to do at the time, drop it, and not receive a failing grade. You can also add new classes before the deadline, but be careful, if you join a class too late, you could fine yourself extremely behind everyone else.