"Submit Video" button is added specifically for guests. See Top Menu "Submit Video".
Guests can submit videos from many websites (i.e., YouTube, Google, Metacafe and much more). All they have to do is provide the link (URL Address) and the administrator will add the video.

Please note that "Submit Video" option is only for Guests. Registered Users can add their videos from YouTube, Google etc using "Add Videos" button OR they can upload their own videos using "Upload Videos" button (See Help for more info).