Here are some examples:
* Correct: Math is my favorite subject.
* Correct: I took a course in English literature.
* Correct: I'm studying at University of California, Berkeley. (UC Berkeley is a proper noun, so "C" and "B" are capitalized)
However, if they are not at the beginning of a sentence or part of a proper noun, you wouldn't capitalize them:
* Correct: I enjoy studying math and English.
* Correct: I took two classes: math and English.