Is the ab-slide the thing with a cushion for your knees and then a piece that you balance on, then roll out and back on it?
If that's the name of it, my trainer has me working out on it at the gym. It is part of my ab-circuit. I don't know the name of it though.
If it's the same thing it's really easy to use.
You sit on your knees, graps the handles, roll out so you are in push-up position on your knees and forearms. Hold it there for a couple of seconds, then roll back to your start position where you are sitting back on your knees. Repeat. Very simple, but the key is to hold the push-up position (this kills my abs).