If you have an iPad Air or older, there is a switch on the side of the iPad that can control two functions, either Rotation Lock or Mute. Rotation Lock freezes the screen in one orientation and doesn’t allow you to rotate, whereas Mute will stop all sound emanating from your iPad.
To choose which, open the Settings app, select General, and find the Use Side Switch To section.
Select your preference for the side switch. The non-selected option is then available in Control Center.