How can you determine whether your Mac has a webcam?

Run the application Photobooth (in the applications folder) if you can see yourself there is a camera built into your Mac (all the recent versions of the Mac will have a camera). if you cannot see yourself, or you do not have Photobooth, then you do not have a built in camera but you may have an external camera which will be obvious and will need to be plugged into your Mac for it to work.