Ensure the "Camera" toggle is green (on) on top left Your browser may ask for permission and offer drop-down menus to select the correct camera and microphone. Be sure the correct ones are chosen.
Otherwise, in the preview of your cam, click the "gear" or "sprocket" icon. In the box that appears, choose the correct camera and microphone. This means the video/audio source you've chosen is not correct/not broadcasting any media to our site.