As simple as it sounds, taking screenshots on Android smartphones is really very easy. In most phones / devices with Android, no need for an application or rooting to be able to take pictures, especially if the device runs on Android 4.0 (Ice Cream Sandwich) or higher.
To take a screenshot on your Android device
Press and hold the power button and the volume down button. Release the button when you hear the startup sound signaling screen was successful.
There are Android devices that are configured to operate differently. For them, use the power button and the key to the house to take possession of the display / screen.
If that does not work
If the device runs on Android 2.3 or one of the more Android versions that do not come with pre-installed screen capabilities, you must install a screenshot of the application. Note that most of these applications require rooting. A screenshot is recommended ultimate screen applications and can be found in Google Play Store.