There are many methods on how to take a screenshot on your android devices. See below on how to do it:
For most Android devices, the most common way of taking a screenshot is by pressing the Power Button + Volume Down at the same time.
If your device has a physical home button just like with Samsung Galaxy Tab 4, taking a screenshot is different. Hold down the Power Button + Home Button together and this will trigger a sound when capturing the image on your screen.
The screenshots you have taken will go to your gallery for viewing.
As there are lots of manufactured Android devices, some of specific devices has their own special way of taking a screenshot aside from the Power Button + Home Button or Power Button + Volume Down combination. You can see them in the Settings in your device under the Gestures or Specific Customized Gestures Settings.