1) Make sure that you have upgrades your account to support video chat.
2) If you cannot see yourself in your avatar area, click the wrench icon and make sure your camera is selected.
3) If your opponents video is stuck on "Loading", turn off chat and try again.
4) If the sound echoes and/or has feedback, your mic is picking up the sound from your speakers. Try using headphones or turn down the volume.
5) It is possible that a firewall is blocking the connection. Configure your firewall to allow the connection.
6) It is up to you to troubleshoot your own system. Try another location or another computer. It can be a process of elimination to find the problem.