The xfdesktop application manages the desktop backdrop. It sets a backdrop image and/or color and it can pop up an applications menu and a list of all running applications when you click on the desktop with the right or middle mouse button respectively. As of Xfce 4.4, xfdesktop also draws icons on the desktop.
The xfdesktop package installs a settings dialog for use with the Settings Manager. From this dialog you can change the backdrop image and color and change settings for the menu and the window list.