Things You'll Need
Instructions
Close "World of Warcraft" entirely.
Download the add-on or add-ons you want to install from a website such as WoWInterface or Curse.com. Save the files to a location you will remember, such as a folder on your desktop.
Navigate to the folder where you have installed "World of Warcraft." If you are using Windows XP or earlier, the default "World of Warcraft" folder is "C:\Program Files\World of Warcraft\," while if you are using Windows Vista or newer, the default folder is "C:\Users\Public\Games\World of Warcraft\." If you are using a Mac, the default folder is "Applications\World of Warcraft" on your main hard drive.
Navigate to the "Interface" folder inside the "World of Warcraft" folder. If this folder doesn't exist, create it.
Navigate to the "AddOns" folder inside the "Interface" folder. If this folder doesn't exist, create it.
Extract the add-on or add-ons you downloaded to the "AddOns" folder using the file compression program. Each add-on should be contained within its own individual folder inside the "AddOns" folder. For example, if you are installing the "AtlasLoot" add-on, the files for it should be located in the "World of Warcraft\Interface\AddOns\AtlasLoot\" folder. Your file compression program should be able to do this automatically.