* Send to existing bus (which is checked)
This allows you to choose a bus that you already have in the project. If you want to use a bus you have alread create to send the output of the Send to use this.
* New Bus (new bus options - Stereo or Surround)
This will create a new bus for you and automatically route the send to it. Use Stereo unless for some reason you need a "Surround Bus" (which is for 5.1 movie type surround sound which you likely don't want)
* Bus Option (which has my interface: Focusrite USB 2.0 Audio...)
This, I think, is just giving you the option to route out to your hardware instead of inside your project. It's for things like Headphone mixes or alternate Monitor configs (I think... don't quote me on that)
* Bus name
This is porbably just the option to name your new bus if you used the "New Bus" option. Can't remember.
* Choose Effect
This allows you to insert an effect (or multiple effects IIRC) into the FX Bin/Rack of the target bus... such as reverb. THis is just a convenience option for setting up reverb/compression busses.
* Pre Fader
This will set the Pre/Post Fader status of the send. Pre Fader = The output from the send to the bus will not be affected by any changes you make to the Track Fader on the TRACK the send appears on (this is usually what you will want). Post Fader = The track fader will affect the output level of the signal coming from the send into the target bus.
* Match Track's Pan and Gain
I've never really seen/used that but it sounds like it just sets your Send's Pan and Gain levels to the track's pan and gain levels. Seems kind of useless but maybe helpful in SOME cases. Meh\
Cheers.
Edit: BTW... all that info is all in the Reference Guide and likely much more informative/concise than what I just posted above. It is worth a look if you really want to understand these things.
Also it should be noted that the Sends modules in X3 look different than the one in John's most recent pic. There were some improvements/changes to Sends in Sonar 2015 so your sends will look a little different than that. They still work the same more or less (AFAIK).