Locked in portrait mode

From the top right hand corner of the iPad screen swipe down to open Control Center. See the icon with a lock in it surrounded by a circular arrow. Tap that icon to return rotation to the iPad.

Note: Not all apps rotate

Try the process bobseufert recommended.

Swipe down from the upper right corner for the Control Center and turn off lock rotation.

You're welcome, try a reset. Press and hold both the home and power buttons until the Apple logo appears. Release both buttons. Wait until your iPad starts on it's own.

Glad it's working for you now.