You can take screenshots of the current screen you are viewing.
Via a shortcut
Press and hold the Power/Lock key and the Volume Down (-) key at the same time for at least two seconds.
• Screenshots can be viewed from the Screenshots folder in the Gallery.
On the screen where you want to take a screenshot, drag the status bar
When the screen is turned off or locked, you can access Capture+ by pressing the Volume Up (+) key twice. To use this feature, tap Settings General and turn on Shortcut keys.
• See Writing notes on a screenshot for details.