Locking rotation on iOS prevents apps from responding to sensors which detect device orientation. This is useful when reading, for example. With the release of iOS 7, the rotation lock toggle has been moved to Control Center.
To access Control Center and lock rotation in iOS 7 follow these steps:
1. Swipe up from the bottom of the home screen to bring up Control Center.
2. The top row of the Control Center shows 5 circular toggles.
The furthest right icon looks like an arrow around a padlock - touch this icon to enable or disable rotation lock on your device.