Find the screenshot as a .png file on your desktop.
Press the “Print Screen” (often shortened to “PrtScn”) key located on your keyboard. (Typically located on upper-right corner of keyboard); If on a laptop, you may need to press the "Fn" key along with the "Print Screen" key.
Open Paint, and click the Paste button located in the upper-left corner of the program (alternatively, press "Ctrl" + "V" on your keyboard).
Save the screenshot by going to File > Save As
iOS - Apple Devices
Press and hold the Power button
Immediately click the Home button, then release the Power button
Find the screenshot file within the Photos application, then Albums and tap Screenshots.