Compression 101

Btw, you don't cut by 2dB for every 1dB that goes in (example given earlier). A ratio of 2:1 means that for every 2dBs that goes in 1dB comes out.

thats what I meant to say.

I mainly use it on kickdrums, snaredrums, bass and vocals. I use it more to 'correct' stuff instead of altering the original sound.
Each track has it's own compressor settings.
Usually I do this during the mixing stage.

Like a watch, I don't know how it works but I do know how to use it if I want to know what time it is.