Send tracks on the mixer are just like auxilary busses on a real mixer. the idea is you put an effect (or effects) in it, so you can give multiple tracks the same effect, without having to load a new effect instance for each track.
you should use effects which can be used as send effects, which means there is the option of having no dry signal coming through it, just the wet signal. (wet signal == just the effect). Any selfrespecting delay or reverb plugin has this. (try a fruity delay 2 in it, notice the dry and wet knobs, thats right, if its in the send, turn the dry knob all the way off.).
Now as far as actually doing this and how to do it, i gotta go with my man above and say read the manual, its in there.
Peace
