First, do the
Menu>Menu>System>Scroll down to Screen Capture and enter thing like GoneCrappieFishin said.
Then anytime you see something on the screen go by that you want to take a snapshot of, push the "power" button quickly once and you will see your screen freeze. This is the unit saving your snapshot to Files.
Anytime you power the unit down, when you bring it back up you will have to turn on the screen capture to be able to use this shortcut.

