question for the producers/engineers out there

ok, basically when trying to mix my tracks i wanna make shure that nothing goes above 0dcb, so i always put a decibal meter on my master track to make shure nothing clips, but usually im almost ALWAYS above 0, usually its my snare or some other percussion noise that takes me over, but if i lower the volume to much, or try to compress it to the point that ill go back to an ok level it always sounds way too low, so then i tried not lowering the individual components but putting a compresser before the DCB meter on the MASTER track, so now the meter shows peaking EXACTLY at 0.0 but the actual volume dosent change when i turn off/on the compressor, just the readings...

so this is my question: how come when i turn on the compressor on in the master track the readings go to good levels, but the volume dosent change?

someone please help me, i am so confused, i thought compression involeved limiting peaks and that would change my volume, but it dosent seem to...and how do the pros get there samples and drums so damn LOUD without clipping?