In the users listing, click on the webcam icon next to a user's name to open their cam. The users listing is shown on the right hand side of the screen (if hidden, press the "<" arrow to open it).
In the room, you can click on the webcam icon next to a user's name to open their cam.
If their cam is green, it is public and anyone may view it. If it is red, it is set to private and they will have to approve your request to view it.