You can take a screenshot by holding down the power button and the volume-down button simultaneously. Hold these buttons down until your screen flashes and ‘grabs’ whatever is currently showing on your screen.
To view your screenshot, go to the Gallery app, then look for the ‘Screenshot’ album. Tap it to open it, then tap the screenshot you took to view that screenshot. You can then email it or share it.
You can also find your screenshots when connected to a computer via USB by navigating to GoTab/GoFone > Pictures > Screenshots