In the U.S. the year generally starts in the fall which is around august (many colleges will not allow entrance at any other time than the fall). Some colleges have winter interim classes (like a week long class). Then you've got spring classes. Some colleges have spring interim classes over spring break. Some have summer interim classes at the beginning of summer. Then many offer summer classes. And so on and so forth. It depends on the school, on the class, etc.
It's all different. My spring classes start on Valentine's day. They'll end June, Summer will start the beginning of July, and Fall will start the end of August. Look up the college's registration dates on it's website.
It depends on where your going, best thing to do is to go to the college website and check out their squedule or call them to find out.
Its generally fall classes, spring classes, and summer classes (which some colleges dont offeer).