Where are you trying to rotate, Karen?
Not all Apps support auto-rotation.
An example of an App that does though is Messages.
If it's not rotating into Landscape when in Messages, do you perhaps have it locked on Portrait?
Swipe upward from the [HOME] button & you'll see a bunch of toggles.
Make sure the icon that looks like a lock with a circular arrow around it is not lit up. If it is, tap it to unlock it.