Hi,
You don't need any license for Video Advantage.
You might have some issue getting Video Advantage working with your PC camera. Its best to use the Video Advantage Camera instead of the PC camera.
As to how it works, you need to plug you PC into the phone. Enable video on your phone from the CUCM. If you have seperate Voice and Data VLANs make sure there is a route between the 2 vlans. CDP is enabled on the phone.
Thanks,