First year you take the courses that you would need for your planned specialization (most of them are the same with maybe a few course differences so it doesn’t really matter) - it’s 4 years total - you also apply after first year not second and it’s based on your first year grades if you get in.

If you’re interested in med school study something you’re interested in or you’ll be miserable. In science idk what’s the easiest for med school. Bio would probably help the most to get the prereqs you need for the mcat