What does the lock symbol by the battery icon mean

If you see a lock icon in the upper right corner of the screen - then the screen orientation is locked. The screen orientation can be controlled in two different ways.

Try the side switch above the volume rocker first and see if that unlocks the screen. If that doesn't do it, double tap the home button and swipe to the right and look for the lock icon all the way to the left.

Check to see if your screen orientation is locked.

It's the button top right side of your iPad.

See p. 12-13 of the User Guide.