Android: Hold the power and volume buttons down for a second or two. When the screen flashes white, the screenshot has been saved to your photo gallery.
iOS: Press the Sleep/Wake button (the button on the top or right side of your device, depending on the model) and then press the Home button. The screen will “flash,” and the screenshot will be saved to your Camera Roll and the Screenshots folder. On iPhone X (which does not have a home button), you’ll need to press the Sleep/Wake and the volume up buttons simultaneously.
Windows: For desktops, pressing PrtScn + the Windows key will take a screenshot and save it to your Screenshots folder, in My Pictures. On laptops, press PrtScn + Alt + Windows to perform the same function. To capture a specific part of your screen, use Windows + Shift + 5, which will allow you to draw a box over what you would like to screenshot. A successful screenshot will be indicated by a screen “flash.”
MacOS: To take a screenshot of the entire screen, press Cmd + Shift + 3. To capture a specific part of your screen, use Cmd + Shift + 4, which will allow you to draw a box over what you would like to screenshot. These screenshots will be saved to the desktop.
Chromebook: Hitting Ctrl + the Windows Switcher key will take a screenshot of the entire screen. For a precise shot, use Ctrl + Shift + Windows Switcher. These screenshots will be saved in the downloads folder. However, they will not go into your Google Drive unless you copy them there.
Adapted from https://www.pcmag.com/article2/0,2817,2475902,00.asp.