If you have an iPad Air or older, there is a switch on the side of the iPad that can control two functions: Orientation Lock or Mute. Orientation Lock freezes the screen in either Portrait or Landscape and doesn’t allow you to rotate, whereas Mute will silence alerts and sounds on your iPad.
To choose which one you want to side switch to control, open the Settings app, select General, and find the Use Side Switch To section.
Select your preference for the side switch. The other option is then available in Control Center.