I need to some basic information about amps

Allright.....i'm new to this forum and pretty new to car audio systems in general. I am interested in putting in a computer in my van but I am also interested in just uprgrading the speakers first. The only problem is that i want to put new Xlpod 6 X 9 in but they require a minimum of 75-100 watts to run. The cd player i have right now outputs 50 watts for 4 channels <pretty normal from what i understand>. This leads to the fact that if i want to put new speakers in, the i will need to get a...or some amps to power the speakers.

So i started searching around on the internet for amps and what i was looking for was something like an amp that had like 150-200 watts on 4 channels <150-200 on each channel>. So I started searching the internet for something between a 600-800 watt amp. I kept finding that the amps would say 800 watt 4 channel amp, but then it would say something like 100 watts per channel, or 2 150 watt bridged channels, or something of that sort. This brings me to my question.....when it says how many watts are per channel, is that a minimum or is that all that it can output? What happened to the other 200-400 watts?

If my question isn't exactly clear then tell me so and i will try and clear it up a bit.

THANK YOU!!!