Have you read the help files? They actually cover this pretty well (Either for ROBO Master Pro, or for Cutting Master 2).
But first thing you need to do is align your KNIFE blade (not laser) up with your first (lower left as you're looking at your machine) registration mark. Which way you do it depends on the type of reg marks you are using. If they're like corners of a frame, then you make sure your knife blade is lined up to the INSIDE (toward your design) of your reg mark. If they look more like printing reg marks (the sides of the reg marks facing AWAY from your design), then you would place your blade toward the OUTSIDE of your design.
Hmmm...I might need to draw a picture here...
You can manually move your blade with the arrow buttons on the front of your plotter.
If that was too convoluted, please let me know and I'll show a diagram of where your blade should be lined up.
