Taking a screenshot on your Galaxy S4 is very easy and quick. There are two options on taking a screenshot.
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.
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.