To include the image in a page, use a link in the form [[File:File.jpg]], [[File:File.png|alt text]] or [[Media:File.ogg]] for directly linking to the file.
If you are uploading a screen-grab from a game, or other pixel graphics, always use a lossless format like png. Also if the image is small (like an 320x256 arcade game screen-grab) consider doubling the size (with no scaling filter), so that it is more easily viewable on the image page. See Image:Bomb_Jack_title_(Arcade).png for an example of this.
If you wish to upload an archive or other non graphical file, then please instead consider getting it added to the ExoticA ftp file archive. More details can be found on the Help:Editing Page.