Go to the page/screen you wish to screenshot
Hold down the 'home' button and the 'sleep/wake' button simultaneously.
When you successfully take a screenshot, you should see a white flash and, if audio is on, hear the camera shutter sound.
To access your screenshot, go into 'Photos' from your home screen.
iPhone X and other Home Button-Less Models:
Certain models of iPhone now don't include a home button! In this case, you should press the 'sleep/wake' button and the 'volume up' button simultaneously instead! It should otherwise work the same.
If you're trying to screenshot a Windows desktop, click here
If you're trying to screenshot a Mac, please click here instead!