This very much depends on your college. In my college (Humanities and Social Sciences) there are a lot of general education requirements (math/science, social science, humanities, language, and the arts). For your major you generally have several core requirements and several electives. You get an academic advisor when you enroll and he or she helps you register for classes and decide on what your major will be. Once you declare your major, you get a major advisor who helps you map out the rest of your courses. If you have any additional majors or minors you are assigned advisors for those as well. Carnegie Mellon is definitely an academically rigorous school, but it's not competitive at all. It's actually a very collaborative environment, and students tend to work together on assignments.