There are just some times when you want your iPhone or iPad screen to quit moving from portrait to landscape with your slightest move. This can come in especially handy when you are reading a book. It’s really east to lock and unlock the orientation of these devices.
Tap the Home button twice. Then swipe the bottom of your screen left and the bar at the bottom of this screen will appear.
To remove the lock, follow the steps above and tap the button again.