Things have changed a little since my day, but . . .
Everyone -- regardless of major -- takes a "core curriculum" of courses. Some are identical, regardless of major, such as leadership, seamanship, law for the jr. officer, etc. In addition, everyone must take other "core courses," that are "weighted" in term so difficulty depending on major. Some of these are physics, and electrical engineering. For that latter, non-engineers take "wires" (the easier course) and engineers take "cables" (a more difficult version).
Plebe year, everyone takes the same courses, unless you've validated. Those include (generally) English, history, chemistry (w/lab), calculus, and then seamanship/navigatio and something else.
Youngster year, everyone continues a full year of advanced math and physics. There have been some changes in the later years, so I'll let someone else tackle those.
If you don't validate, you'll start courses in your major as a youngster. There are certain required courses in your major and the rest are electives. In my day, Group III ("liberal arts") majors had to take or validate 2 full years of a language. Not sure if that's still the case.