Game addons do a lot of different things within the game.  Most of them help you manage your character in a special way. Others help with the game play in special ways.  Listed here are some we have found and would recommend for use.

All addons are installed in a sub-directory of your World of Warcraft install directory.  Mine is:

D:\Program Files\World of Warcraft\Interface\Addons

If you are using Cosmos then you will want to put a file in that directory that will tell Cosmos to not update or delete your addon. This is done by making a zero length file with the addon directory name with the extention of NOPATCH.