Hosts and Guest Presenters: Before going on camera, consider using Audio & Video Options to preview everything.

Click the 3 dots on the top navigation:

Options

Under Audio & Video Options, you can preview how you look on webcam and make adjustments to your background. You can also check your mic to ensure it is working or choose a different mic and test your speakers for sound:

Options2

If you find your mic or speakers are not working, click on DIAL-IN FOR AUDIO and join on the telephone.

Alternately you may choose from the navigation menu to Switch to Phone as well:

Phone