Track Output vs. Send

Hello,
 
Each track can route through the 'output' and/or through the 'send'.  What is the difference between these and when is one better than the other?
 
Thanks!

Ya, the main difference is that a "send" is a copy of the signal routed to...something other than the main outs (generally speaking, a buss).  As Greg said, it's often a reverb or a delay, though there can also be other cool effects like a compressor for parallel processing (use part processed sound and part dry sound to make a final sound).  

Here's a quickie diagram I made in paint to try to illustrate.

sends - it's a big subject and these 2 have covered some good stuff.

but there's still a lot more to it also.  for example, you don't have to send 100% signal to the bus and that's very helpful for stuff like reverb or chorus FX.  you can set up a REVERB BUS, set up a reverb with 100% wet signal, 0% dry (don't allow the reverb plugin to mix any of the dry back in, for a send bus you want only the wet signal going back out because you already have the dry signal on the track output).

then you set up sends from each of the tracks and send those to the reverb bus.  you can vary the level of the send to create the "stage space" in your mix.  for example, if you want the rhythm guitar to sound further away than the lead guitar, then you would send more signal to the reverb bus from the rhythm guitar track than you would the lead guitar track.  since the reverb bus is 100% wet, it's ALL reverb, so the more reverb there is, the further away it is in the sound stage.

then you'd do that for all of your instruments.  more send to the 100% verb bus means further away, less means closer.

this is just one major example.

Beagle is absolutely right, and it's something I left out. When you're mixing in effects from an effects send, you should make sure the effect is 100% wet.  I'm not entirely sure what MC6 allows, but you can send something different than full volume to your sends in X1, and if MC6 allows that then for sure you want to maybe send less to the reverb buss.

And, again at least in X1 and maybe MC6, you can also send pre-fader, meaning using the fader on the main track doesn't affect what's sent to the buss...pre-fader can lead to frustration with reverb and delay, but it is likely exactly what you want if you're doing parallel compression on your drums, because of the way compressors work.  You might get it sounding just like you want and then lower the fader on the drum tracks only to find your squashed signal doesn't sound like it did before.  

OK, so you can do pre/post fader and adjust send levels then, that's good news.

I was pleasantly surprised when I got X1 essentials as an upgrade from Guitar Tracks (after I bought a VS-20, I couldn't handle the layout even as a secondary machine's DAW) so I could have concurrent X1 installs on both my laptop and desktop.  Essentials, aside from missing PC and some plugins (and audio snap, and v-vocal, and a 64-bit binary...), is very much like Producer.