There's several different ways to do this. The most obvious is the "M" in the Timeline Panel or Audio Mixer Panel.
However, you might be wanting to mute just a clip. There's a bunch of ways to do that, too. I like to use the Mute effects from the Effects Panel. It's under Audio Effects. Then when you drop it onto you audio clip, you have to switch the "0" to "1." The "0" and "1" toggle the mute on and off.
Again, there are a ton of way to accomplish this, I just listed two.