to my understanding, the note variation slider can quickly change the value of a sound's filter, decay, attack and most imp. in my opinion, the pitch. i've heard it can be similar to pitch control on a record player, but not quite. Just press shift and note and then assign a pad to the slider and play around. You can also set it so that u can change it's value "after" laying the note. Notice the difference between the note button being lit or unlit.
As far step editing, you can accurately pinpoint the positions of notes to the tic. U can use step editing to place you snare on "2" and "4" or rec your notes live then go back and edit something that is slightly off. You can also change each specific note's value for duration, decay, filter, tune, etc... I'm sure there is more but these are the basics. Play around w/ it.