Music composition is a very specialized course that teaches you just that: how to compose. Some basic music theory and harmony is essential to follow such a course. Music theory is more of a .. "how it's done" and "how to get started" course, but will build up to really specialized study, if you care to pursue one.
If you want to be a songwriter, it's another thing, Composing is for compositions, Songwriting for songs, and theory, is, well, the base for all of this. You can't do composition without theory.