On a laptop, you can use the keyboard shortcut combination of Fn+F7 (F7 might differ depending on the laptop model) and for a desktop, you can always use the power button.
You can always create a shortcut and assign a keyboard shortcut to a black screensaver, use this path:
%systemroot%\system32\scrnsave.scr /s
This will not turn off your screen but make it completely black.