Mastering is an entirely different beast. Go to the mastering section to read about it or just look it up in your fav. search engine.
Tweaking everything is mixing: setting levels, EQing, panning in the stereo image, EQ carving, building dynamics with the introduction of some of the stuff you;ve tracked, lowering otehrs etc etc.
YEP the drums hurt - REALLY hurt. tame the top end if nothing else.
As you are new you really should post your tracks on a streaming site like reverbnation, soundcloud or sopundclick. Folk'll be happier to download to listen AFTER you have established a relationship with them and after you've provided feedback/critique/commentary on their stuff.
Ouch, I had to stop listeining about 30 secs in to the drummed section and my head STILL HURTS. It's hard to critique the music when in pain - but the pain def says the mix needs WORK.