One of the iPad's most convenient and intriguing features is its ability to sense its own screen orientation and adjust automatically to portrait or landscape mode based simply on how the user is holding it. You can tell the iPad to stop sensing and accommodating screen orientation, by flicking a switch to lock the orientation in place.
Hold the iPad in the configuration, portrait or landscape, in which you want to lock the screen.
Locate the screen rotation lock switch, directly above the volume controls on the right hand side of the iPad (when viewed with the Home button on the bottom).
Switch the screen rotation lock button to the down, or locked, position to prevent the screen from rotating with the iPad. When the lock is activated, a lock icon appears at the top of the screen.
When you no longer need the screen locked, move the lock switch back up to the free position.