Clicking on the audio icon
To mute your audio, click on the green microphone or handset icon (depending on whether you are connected to conference audio via computer or a telephone, respectively).
Once muted the icon will appear with a line through it. Click again to unmute your audio.
Using the Audio Panel
You can also use the Audio Panel to control your microphone. To open the Audio Panel, click on the drop down menu icon just to the right of the microphone or handset icon on the top menu bar. See "Audio Panel" for details.