cable help

[cwr89]

I have been looking at mixers. I have desieded on the yamaha MG12/4

I am going to have 4 mics hooked up to the XLR jacks.

I also want to have 3 line ins hooked up to it. are channels 1 - 6 the microphone channels? and it says that only channels 1-4 have line in.

first of what is the difference in RCA and TRS cables? is it that rca is mono and trs is stereo?

if that is the case. could I run a cale that is rca on 1 end out of the line in on my amp into trs, then connect it into the mixer??? (to do this, I would look at radio shack to see if there is a premade wire for that, if not, i would make my own using the 1 rca plug and some instromant cable, split the cable and have half of it hit right channal half on left channel)

help I am confused!