I've never seen one of these before.
I think you've probably pretty well figured out how to use it. I might consider using a rod to roll the quilt up on as it's completed and stored in the "tray. I think the grey tubing that's laying in the front black channel, is probably intended to hold the quilt "sandwich" in place as you quilt. Get yourself some inexpensive materials, and try it out. As you work, the function of the various pieces will probably become apparent. Good luck. Jim