Have fun!
I'm not sure what they mean by tray either but I am thinking it is the piece that hooks on to the bottom part of your machine (where the feed dogs are located) to increase the flat sewing surface of your machine? Just a wild guess but that certainly makes a difference when trying to FMQ and machine quilt. Many sewing machines come with one it is like a big U shaped unit that latches on to that bottom arm (the part of the machine you would but like a sleeve around when sewing clothes) I hope I am making sense.