Ok ram capacity does not really have to do with much performance. if you have enough ram to cover everything you are running, you will not have any lag. if you are nearing the max of your ram, you may see some laging or freezing. Id recommend opening task manager (ctrl + shift + esc) and go to performance tab. Look at memory usage, then open EVERYTHING you can think of you would ever run, then look again. If your not atleast at 90% or more, you dont need more ram... 4gb in most cases is mroe then enough for most anyone for gaming,
Channels. Well to explain it more, dual channel means 2 sticks that will work together for better performance. But to get use of the dual channel your motherboard needs to support it (really now days all do), and you have to put them in the right slots. (they are all color coded now, ie, match the 2 red slots for dual channel memory).
The only motherboard that supports triple channel is the socket 1366. buying triple channel will have NO performance gain over dual channel if you dont have a triple channel motherboard/cpu.
when you see quad channel, that just means 2 sets of dual channel. because say if you buy ddr3 1600 @ cl6, the only dual channel set of that is 2x2gb (4gb). but it only can only run at ddr3 1600 @ cl6 with 1 set. If you say wanted 8gb of this, and bought 2 sets of dual channel, it probably wont be able to run all 4 sticks at 1600mhz with CL of 6. BUT they may have a quad channel set with 4 2gb sticks that can run all at 1600mhz @ cl6. (and that will be VERY expensive lol)
hexa channel is the same as above, but 2 sets of triple channel that will be able to run all at the rated speeds.
Ok now as for speed and CL(cas latency) that determines the speed and latency of the ram. the higher the mhz, the more data it can process in a time, but the timings (cas latency) are basically how long it takes to do it. So the faster in speed you go, the longer/higher the cas latency becomes. So you usually want to aim for the best speed with the lowest latency (really the best if pretty much ddr3 1600 @ cl6).
To get the sticks running at the rated speeds you usually have to manually set them in the bois, and usually have to play with voltages.
But really ram speeds dont affect gaming that much. your money would be better off spend in a better cpu/graphics card then in ram.