Been hearing abit about compression and realised I have no idea about it. If it makes a difference, it was referred to when talking about the popping sound coming from the exhaust while decelerating while in gear (like a manual.. backing off accelerator without pushing in the clutch pedal)...

What is compression about? What are the benefits of having more/less compression? How do you get more/less compression?

compression is how much the piston in your engine compresses the air/fuel mixture once its in the cylinder.

I feel really lame for putting this here, but wiki is your friend and even has a moving diagram lol.
http://en.wikipedia.org/wiki/Internal_combustion_engine

With reference to static compression it is a measure of what the volume of your cylinder (including head and piston crown) is at BDC and TDC. So for a compression ratio of 9.5:1 it means the ratio between the pressure at TDC (when compressed) is 9.5 times that of at BDC (ie atmospheric). However this is in a perfect situation; in reality it doesn't quite work this well.

Dynamic compression takes into account overlap of cam etc.

To increase compression you can run a thinner gasket, get metal taken out of the head (although this can play havoc with timing) or better yet, get a bottom end rebuild with higher compression pistons. You will most likely either have to run better fuel or get a tune.

the popping your talking about is just unspent fuel igniting in the exhaust, im not sure if that is directly related to a higher compression ratio. some people call this engine braking "compression braking", possibly this causes some confusion.