In console view (I prefer to do it there - others may disagree), insert a new Stereo Buss. this should route directly to your Main Outs/Interface
Now route all of the outputs of your tracks to the Master Buss
You can now insert plugins on your master buss and get the levels up to something approaching commercial levels, but please, don't overdo it - the more you increase the level, the more you'll decrease your dynamics in the song which eventually results in a fatiguing sound.