Stop automatic rotation
Prevent screen from rotating
Open quick settings and turn 
Auto-rotate off.
In this mode, you can manually rotate the current app. Turn your phone the direction you want, then touch 
in the corner.
Allow screen to rotate
To allow rotation for all apps, open quick settings and turn Auto-rotate on.
You can also adjust this in Settings > Display > Advanced > Auto-rotate screen
TipIf your home screen isn't rotating but Auto-rotate is on, then check your home screen settings. Touch & hold a blank spot on your home screen, then touch Home settings > Allow Home screen rotation.