1

Press the Power and Volume Down buttons at the same time.

Note: Some devices need you to hold the Power and Volume Down buttons until the screen flashes. If pressing the buttons doesn't work, try holding them for 1 to 2 seconds.

Note: If pressing or holding those buttons doesn't work, then your device manufacturer may have another method. Check their website for more information.

2

Your screenshot can be found in the Screenshots album in the Photos or Gallery app.