If your microphone is not muted, but you are still having issues, click on the "Settings" on the upper right corner of the page. Make sure that your camera, microphone and speaker devices have been selected for your system.
Press the "Test" button to confirm your speakers are working correctly. You can talk into your mic and you should see an orange "volume bar" under the microphone box.
If you are connecting through a web browser, you need to allow your browser to use your camera and/or microphone. Click "Allow" if your camera or microphone is not working.
If you are still having trouble with your video or camera, please write to firstname.lastname@example.org for more assistance.
In the meantime, check out this video tutorial about how to join your class on the web.