When you hit PrintScreen key, windows will take screenshot on the monitor and copy it to clipboard. But if you have dual monitors setup, you will find screenshot of both monitors are captured. You might wonder how to just capture the single screenshot on the monitor you are working on.
The answer is ALT + PrintScreen. Note that it will take screenshot of the active monitor on your desktop, the one has keyboard/mouse focus.
In addition, you can use CTRL + ALT + PrintScreen to capture the active dialog box or menu on your desktop.