Once you've created an AutoCollage and it is displayed in the AutoCollage View pane, you can set that collage as your desktop background.
To set the displayed AutoCollage to your desktop background, click on the Desktopbutton. The AutoCollage is saved to a temporary location, and Windows tiles it to make your new desktop background.
To create a collage specifically to use as your desktop background, you should set the Output Size to Screen Resolution in AutoCollage Output Options, and then create a new AutoCollage.
See also: Setting AutoCollage Output Options