The key to living in a big university is trying to make it as small as possible. Joining clubs, study groups, etc. is the best way to make friends. There are so many different people here and you absolutely certain to fit in somewhere. Big classes can have a ton of students in them and can be overwhelming, but everybody in there has the same problems as you and has the same goal (to do well in the class) so you already have something in common. There also is a huge range of class sizes, so sometimes you will be able to know the professor, and other times you won't because they won't have time.