does your mixer have a "aux send" come out of the aux send, into the in of the effects then come out of the effects into the "aux return" then to aplly that effect to a channel, simply trun up theaux knob on that channel.
to hook up a compresser there are 2 ways to do this:
1. does your mixer have "inserts" at the top where you plug in the mic? if it does, then get you a "y-cable" from radio shack and do this: plug the single part of the y cable into the insert. the plug the v part of the cable into the compresser. (the y cable should have the ends marked with in or out) plug the "in" plug, into the in on the compresser and then, plug the out plug, into the output of the compresser. (sometimes the compresser's in's and out's will be marked: tip(in) or ring(out) )
2. hook the mic into the compresser's input the get a cable and plug it into the compresser's output. from there plug the cable into the channel.
this works for me and i'm only 14 years old. so i'm sure that it can work for you too.
good luck and welcome to homerecording.com,
zeke