You can set some options on each tray. To access the options, right click the mouse on the tray and choose the option Tray options or press the key O while the tray is open and active.
Name of the tray : A name for that specific tray. This may be useful, for example, to set a hint on what you plan to put in that tray for this game.
Background : To setup the background for this tray.
Show MiniImage in this game : To tell if that tray must display the reduced image of the puzzle. This setting is only for the current game, see the next one if you want it always.
Show MiniImage always : That box will display the MiniImage always (not only during this game).
One tray at a time : When you open a try any other open will be automatically closed