DevelopersVoice.com

There are many different file types out there. Lots.
Below you will find some information on the various types you may come across when downloading, and what you should do with them.
The guide is just an overview, designed to point you in the right direction - for more help on filetypes and what to do with them have a look at this site
File Types & Tutorials
it contains lots of tutorials and visuals to help.