you have to mixdown your tracks first. you have to make sure that the master output is NOT hitting above -3db at the maximum (-6db is preferable) The way i do this is i mute all the tracks and solo the kick drum, and have that peaking at around -10dbish or there abouts, i then slowly unmute more sounds and adjust their volumes to match the kicks, while always checking on the master output, continue doing this to all your tracks and sounds so that all their volumes are matching up to that of the kick drum, in the process of doing this if your master is starting to creep up to 0db, try eqing some things or lowering the kick a bit more then adjusting everything else accordingly. your aim is to have everything eventually unmuted and the loudest part of your track hitting no more then -3db. you then export this and this the (Mixed down version) you can not play this, it will seem pretty quiet to everything that has been mastered. Now to master a track is a mind fuck, i just follow youtube video's or ask someone that knows how to do it to master for me (you just send them the mixdown and they can take it from there)