Helper applications are programs that you configure to use as viewers. File types are normally identified by the last three digits of the filename. There are different file types for graphics, sound, and video files, among others. An excellent resource for finding helper apps for a particular file is Stroud’s Consummate Winsock Apps List that is available at http://cwsapps.fibr.net.
The site has reviews of all the available helper and explanations of what functions they perform. It’s also fun because Forest Stroud has a myriad of different applications that help you tell the time around the world, compose Web pages, and much more. Forest Stroud also rates the reviews of these applications for you, so you don’t have to!