First off, props to you for advance prep :). Oberlin is a pretty awesome college. I had the same feeling of instant identification when I found out about Oberlin, too.
Most liberal arts colleges in the U.S. require you to take courses outside your major. Different colleges do this in different ways. Colleges like Brown and Hamilton let you take whatever courses you want to, without any restriction. Other colleges have "core" courses that you need to take at some point in your college career. Oberlin has distribution requirements. I'll explain this after I explain how the U.S. system works. I apologise if you already know all this.
Okay, so you need to take a certain number of credits each semester. Most courses are a semester long, and range from 1 to 5 credits (mostly 3 or 4.) At Oberlin, you can take between 12 and 16 credits each semester. (The classes are very work intensive), so usually 4 or 5 classes. Most cases, 4.
The way the major works is that you take a series of courses on the subject. There are courses that are required for the major. For example, the computer science major requires 13 courses. 10 in Comp Sci and 3 in Math. Every computer science major doesn't take the same courses, you have options. Everyone has to take basic Java and data structures, Scheme, algorithms and theory of computer science, but the other classes are your own choice. You can take networks, or you can take digital animation, or a whole host of other classes.
The three math courses required are Calculus, Discrete Math and Linear Algebra, but since a math minor takes only two more classes, lots of CS majors also get a math minor. Besides, math is a lot of fun.
So, the CS major takes up only 13 courses of your 32 (or more) courses. You're free to take whatever you want in the rest. Lots of people, especially at Oberlin, double major. I'm trying to do Computer Science, and design my own major (yeah, you can do that) in South Asian Studies.
Distribution requirements!
So Oberlin has the 9-9-9 rule. Classes are designated Humanities, Social Sciences, or Natural Sciences. You are required to take 9 credits in each of these divisions, in at least TWO different departments. Like, you can't use English to cover all of your humanities requirement, you also have to take a course in another humanities department.
You can't take more than 56 credits in one department, or more than 84 credits in one division. You need to take 9 credits of classes marked Cultural Diversity, and a quantitative proficiency class (class with some math) and a writing intensive class.
This isn't as big a deal as it sounds. You'll end up taking all these courses anyway, and lots of courses give you more than one set of credit. Right now I'm taking a class called "Religion in Modern India", and I'm getting 3 credits cultural diversity AND humanities at the same time.
So yeah, that's how you study different things in liberal arts colleges. For example, this is my schedule last semester:
1. First Year Seminar: Rationality, Objectivity and Truth in Science (philosophy)
2. Physics: The Charm and Strangeness of Elementary Particles
3. Politics: Explaining Social Power - Classical and Contemporary Theories
4. Computer Science: Principles of Computer Science I
I decided to load up on CS / Math this semester, so this is what my schedule looks like:
1. Computer Science: Principles of Computer Science II
2. Computer Science: Computer Organisation
3. Mathematics: Calculus II
4. Religion: Religion in Modern India
I'm probably taking five courses next semester, I'm not sure about my schedule yet.
The computer science department is small, but absolutely great. We have five professors, and quite a large variety of courses, for such a small department. A lot of courses are offered alternate years, so a larger number of courses can be offered. I've taken three classes, and all of them are pretty wonderful, and all the professors are great, and willing to help you out anytime.
Feel free to ask me more questions!