There are several reasons why you might not want the iPad to automatically switch from portrait to landscape (or vice versa) screen orientation. Some apps look better in one or the other aspects and several games really don’t suit landscape mode. Luckily, there is a way to stop your iPad switching screen orientation automatically and keep it fixed on either landscape or portrait mode.
Whilst in any app, double-click the Home button at the bottom of your iPad to bring up the app bar. This shows you all your currently running apps. It also contains some other controls.
Swipe your finger across the bar to the right to reveal several controls at the far left of the app bar. These include Brightness, volume and play/stop controls, as well as the button to lock the screen orientation (the button featuring the circular arrow).
Touch the orientation lock button one to lock the screen in whichever orientation is is currently in. Tap the button again to unlock screen orientation. You can change this at any time, and in any tap.