When you sit down to work with your MacBook Air, a laptop computer made by Apple, you listen to sounds from its built-in speakers or from headphones that you plug into the headphone jack. When you start an application that plays songs such as the free iTunes music application that comes already installed, or when you visit a website that plays sounds, such as a video-hosting site, you'll expect to hear the audio. If you don't hear anything, you'll need to unmute the MacBook Air or turn up the volume.
Press the "F11" key or the "F12" key, located in the top row on the keyboard to turn on the sound if it has been muted.
Press the "F11" key repeatedly to turn the volume down.
Press the "F12" key repeatedly to turn the volume up.