The SWF is the SoftWare File. It has all of the info and things for a game. However, you cannot submit a game unless you made it. Or from what I have been told, you can submit another makers game IF you have the permission from them.
SWF is a file type you can run with SWF player or real player, if you are uploading a game it must be yours. If you are one of creators you should know how to change game format.