If you aren't able to identify your webcam in the list of video devices or not seeing a video preview. There is a possibility your camera isn't active on your machine.
A few suggestions:
Close out any other applications that could be using your webcam.
Unplug the USB cable of your webcam from your computer and insert it into another USB port on your computer.
Restart your computer.
If you're on a Mac, see Enabling Permissions to access your camera.
If you're on Windows, learn how to allow Vast Conference access to your camera.
Still not working?
Refer to this windows article to test your camera:
Refer to his apple article to test your camera: