If you’re using Android 4.0 (Ice Cream Sandwich) or later, taking a snapshot of your screen is now integrated into the operating system. No longer will you need to run an app which may spam you!
To activate the screenshot you just press and hold the VOLUME-DOWN button/rocker & POWER button at the exact same time [this may take some practice to avoid pressing one before the other]. You will see an animation on the screen indicating that the screenshot was saved, as well as a notification icon in the upper portion of your screen.
By default, Android will save the screenshot to your Gallery. To navigate to the screenshot, you can either tap the notification item and go to the picture directly, or launch the Gallery app/icon and tap the ‘Screenshots’ folder to view and share your screenshots.
[And thank you Google!]