Press and release the Power and Volume down buttons at the same time. If it worked, you'll see an onscreen flash, and your screenshot minimized as a thumbnail.
There's a quick and simple way to take screenshots on most Android phones. Press and hold the Power + Volume Down buttons simultaneously. Use the Android Screenshot... · Use Gestures · Use the Quick Settings Menu
Use button combinations. For all Galaxy devices, taking a screenshot typically involves the Power and Volume Down buttons. · Palm swipe method · Voice commands.