As a participant, just click on the Webex link in the invitation.
The Audio Broadcast Panel will automatically pop-up and connect you. Once the meeting has started, you will hear the audio stream from your computer.
It is recommended that you use a headset connected to your computer or mobile device so you don't disturb people nearby.
Audio broadcasting has started
On mobile, using the Webex app, tap this icon at the bottom of the screen.
Mobile app toolbar at bottom of screen
If you close the audio panel, you can restore it in one of two ways: