PC: Hold down the "ALT" key and press "Print Screen" on your keyboard. Then hold "CTRL" and press "V" to paste in to your email or a word document.
Macs: Hold the 'COMMAND' and 'SHIFT' keys together and press the number '3'. Your Mac captures the entire screen and saves it as a file on the desktop.
iOS/iPhone/iPad: Press the 'Home' and 'Sleep/Wake' button at the same time. Your device captures the entire screen and saves it as a photo. You can then find it in the photos app.