As simple as it sounds, taking screenshots on Android smartphones is really really easy. On most Android-powered handsets/devices, you DON’T need an app or rooting to be able to take screenshots especially if your device is running on Android 4.0 (Ice Cream Sandwich) or higher.
To take a screenshot on Android device
Press and hold down the Power Button and then the DOWN Volume Key. Release the button’s when you hear the splashing sound signaling the screenshot has been taken successfully.
There are some Android devices that are configured to work differently. For these, use the Power Button and Home Key to take the screenshot/screen grab.
If this doesn’t work
If your device is running on Android 2.3 Gingerbread or any of those older Android versions that doesn’t come with screenshot capabilities pre-installed, you have to install a screenshot app. Keep in mind that most of these apps will require rooting. A recommended screenshot app is Screenshot Ultimate and you can find it on Google Play Store.