Samsung galaxy tab 3 User Manual page 19

Note: Screen rotation needs to be enabled for the screen orientation to automatically change.
Touch and drag down the Notification Panel, then touch Screen rotation.
Pinch and Spread
"Pinch" the screen using your thumb and forefinger to zoom out or "spread" the screen to zoom in
when viewing a picture or a Web page. (Move fingers inward to zoom out and outward to zoom in.)
Tablet Basics 11