Hi
I think dnarkosis has done an excellent job in explaining the quantize-feature. I just have two or three minor comments:
The Groove-quantize works fine, but the result is often a little hard to predict, so you just have to try. If you use the try-and-fail method, you will get it right.
The "undo"-function on the quantize-function is brilliant. Using this you can try different settings for quantizing, and remove it if you don't like it. The important point is that you loose this advantage if you use quantize during recording. Post-recording quantize is simply best for most situations.
Remember that the XPs have a 96 ppqn sequencer. This means that it has 96 clock pulses (ticks) per quarter note. If you remember that, the rest should be obvious..

Stig