What file extensions are supported?
As far as game files go, you can upload the .swf file if it's a flash game you want to upload. For HTML5 games, archive the files in .zip file and upload that one. (Note: The index.html of your game must be in the root directory of your .zip, otherwise you'll get an error on the game page.)

For image files, you can submit .jpg, .jpeg or .png .