Start -> Settings Manager -> Window Manager -> Keyboard.
Minimize all windows: Ctrl + Alt + D.
Under Ubuntu if you press the PrtScn button, an application starts that allows you to take a screenshot. How to have the same thing in Xfce? First, install the program
xfce4-screenshooter. Then add a new application shortcut:
Start -> Settings Manager -> Keyboard -> Application Shortcuts tab.
xfce4-screenshooter and assign the PrtScn button to it.