Hmm.
Yes, you send to a bus.
Pre and post fader send makes a difference.
A pre-fade send is unaffected by track output volume or effects. You can mute a track, and an associated pre-fade send to bus will still be at full volume.
A post-fade send will be affected by the track output volume.
Either way, as Jeff noted, a send provides a secondary signal path.
My personal favorite use for sends is to define the space around my instruments.
I'll route the track outputs to the master bus (or possibly an intermediate bus), and insert sends to a reverb bus.
This gives me a good deal of control, and I can pull the relatively dry instruments forward in the space defined by the reverb bus.
Take a look at this:
http://forum.cakewalk.com/tm.aspx?m=1302521 It is pretty basic, but it may shed some light on sends and busses.