MyWarCraftStudio is a 3rd party program written by Linghuye for use with the World of Warcraft game files, allowing you to browse through textures, models, maps, and even extracting files from the MPQ client. 


In that way you can for example change the way your character looks ingame. You dont have to download any models, as all models are in you World of Warcraft folder.

WoW Modelviewer is a great tool to use for My Warcraft Studio.