Apple iPad screen will rotate between landscape and portrait mode if you manually rotate the ipad device. By default, screen will automatically rotate as and when you rotate the ipad. You can disable this screen rotation and set it to stay permanently in either landscape or portrait mode while using iPad screen rotation lock feature.
Use Screen rotation lock on iPad [Old method]
To disable and prevent iPad screen from rotating use Screen rotation lock button on the iPad device. Slide the rotation lock down to lock iPad in current screen orientation.
A locked icon will appear in status bar when screen is locked through Screen rotation lock button. You can slide the lock switch up to unlockand enable screen rotation on iPad (the default setting). Simple, isn’t it?
Lock screen rotation [for iOS 4.2 & above]
If you have updated iOS software on iPad device to 4.2 or above, then screen rotation lock will not work. Instead of locking screen, it will mute volume on iPad device. You can find screen rotation lock button within iPad interface (instead of using physical screen lock button). Click here to see button for locking screen rotation in iPad device.