Taking a screenshot on your Galaxy S4 is very easy and quick. There are two options on taking a screenshot.
First option:
As you can see in the first picture, you just have to hold the Power Button and the Home Button at the same time for a couple of seconds, then the screenshot will be saved on your gallery.
Second option:
First go to Settings»Motions and Gestures and enable Palm Motion. Then just flip your hand over the screen to take a screenshot. Simple as that.