Another music major here. Other folks suggesting learning some theory is good for sure, but that's quite a time investment. I'd recommend trusting your ear more than anything. If you have a little piano, just try making chords at random until it starts sounding good. I'm not a pianist and this is how I do my comps. Granted, I can analyze it afterwards, but that only helps me explain the comp to other musicians, it still sounds just as good without the theory knowledge. In terms of producing. Download a DAW (I used audacity until I got ableton) and start looking up tutorials. I can guarantee you there's a tutorial out there for any question you have about any DAW. Your productions and comps won't sound good at first, but don't be discouraged, that's a part of the process (also we tend to be more subjectively critical of our own shit). Good luck! And dm me if you want help or someone else to compose some shit for ya.