You can silence, or mute, a track so that you don’t hear it when you play the project. Muting tracks is useful when you want to hear how the project sounds without the track, compare alternative versions of a track, or try different loops in a project.
Click the track’s Mute button 
in the track header.
Click-hold a Mute button , then drag the pointer up or down.
The Mute buttons of all swiped tracks switch to the same state.
Hold down Command while clicking the Mute button in a track header.
All Mute buttons that match the state (muted or unmuted) of the clicked button also switch to its new state. For example, if you click an unmuted Mute button, all unmuted tracks are then muted.