To supplement what the others have said... once upon a time, when you
pressed PrintScreen, DOS computers would dutifully send the contents of the
screen to the printer. If the printer wasn't turned on, DOS being DOS, the
computer would lock up until you turned the printer on. Many users didn't
know this, and simply rebooted. Or, if the printer *was* on and graphics
were onscreen, it would then take an hour or two and waste a lot of ink
trying to print the contents of the screen.
At some point, the folks at Microsoft (or perhaps at IBM) got tired of all
of the technical support calls arising from folks accidentally pressing the
PrintScreen key, and changed it. So now, instead of printing the screen, the
key now makes a graphical copy of the screen and places it into the
clipboard. (Making this slightly more useful and selective, if you press
Alt+PrintScreen, then only the current window gets copied to the clipboard.)
In order to actually use this key/feature, you have to paste the copy into a
program that can handle an inserted graphic... such as Word (but not
Notepad) or PhotoEditor, etc. And, then print from there.