oh yeah, maybe I should answer your questions too!
Channels are basically left and right. A 4 channel amp would allow you to amplify left and right speakers for the front and rear. A 2 channel amp would allow you to do just one set. There are also Mono amps that are used for driving subwoofers. There are even 5 channel amps that allow you to amp all 4 door speakers and run one subwoofer.
Bridgeable means the amp can be bridged to a lower number of channels at higher power so a 4 channel amp with 50 watts per channel may be bridged down to 100 watts by 2
Other things to look for on amps is power rating
RMS power is the power the amp puts out at 12volts
Most amps also list rms at 14.4 which is really the amount of current that a car battery puts out, contraty to popular belief. This is a critical number and the power rating you want to go by. There is also MAX power which is usually listed at 14.4. This is the amount of power that an amp can put out for a brief amount of time, but not sustain, such as a hard bass note. The RMS power is the amount of power that the amp puts out constantly. BEWARE OF CHEAP AMPS THAT FALSIFY THEIR OUTPUTS ON THE BOX!!! i.e. Pyramid Reputable amps such as Alpine v-12, MTX thunder, Phoenix Gold come with a testing certifacate that shows how the amp actually tested Alpines have been known to test out at nearly double what they are rated on the package while the cheapo's often don't put out half as much as what they say.
