There are some exceptions, but in the vast majority of cases you can take a screenshot on Android by pressing and holding the power button and volume-down button at the same time.
The screen will flash, and a notification will pop up pointing you to the new image in your gallery.
There is a slight knack to this action: press the power button too soon and the display will switch off; press the volume-down button too soon and your screenshot may be marred by an onscreen volume slider.
Using the Home button instead
If pressing the power button and volume down button doesn't work, this is probably because your phone or tablet has a physical home button. Try swapping out the power button for the home button in this scenario.
To take a screenshot, simultaneously press and hold for a few seconds the home button and volume-down button. As in the previous step, the screen will flash to signal to you that the screengrab has been captured, and you'll then be able to access sharing options.
This method has long been the screenshotting process of choice for Samsung's Galaxy S-series, but with the Galaxy S8 no longer featuring a home button you must instead press power and volume down.
Depending on which device you are using, you may find more options for taking screenshots.
Samsung phones, for example, let you perform a palm-swipe gesture to trigger a screenshot. They also offer extra functionality, such as the ability to perform an extended screenshot (Scroll capture).
Some Sony phones offer a 'Take a screenshot' option in the power-off menu - press and hold the power button to access this.
How to record the screen in Android
Screencasts are now possible on all devices running Android Lollipop and later. You may have an app preinstalled on your phone that will do this for you - check before you download another one - but if not simply launch Google Play and search for Screen Recorder.
The app we have used in the past is now called the Riv Screen Recorder. It's free to install, but there are now many other options too.
Simply install the app, click Open, and press the Start Recording button to begin your screencast. Press Stop Recording when you have finished, and the file will appear in the main window with playback, sharing and delete options.
You can use the video editor on your phone to trim the start and end points accordingly.