Press & hold the Power button, then touch Screenshot.
When the screenshot is captured, you'll see 
Swipe the status bar down, and on the screenshot notification:
The easiest way to take screenshots is with a gesture you enable in the Moto app.
To set it up:


To take a screenshot:
Use three fingers to touch & hold the screen.

When the screenshot is captured, you'll see 
Swipe the status bar down, and on the screenshot notification:
Open the 