World of Warcraft has an extremely flexible interface designed to allow users to customize it in a multitude of ways by creating their own addons. While writing an addon is quite complicated, installing and using addons is very simple. Addons are not cheats or hacks, they are condoned by Blizzard, and there are hundreds of them available for WoW. Most people find them so useful that once they start playing with them, there's no going back. Here's a quick guide to downloading and installing addons for WoW.
They typically come compressed in Zip format, although some sites now offer software that manages and updates addons automatically. To work with Zip files, you will need a program like WinZip, WinRAR, or 7-Zip. These are a few of the more popular sites where you can download WoW addons:
Installing an addon for WoW is really a simple matter of extracting it from the compressed file into the correct folder. Within the World of Warcraft folder on your system are the sub-folders Interface/Addons, which is where you need to extract your addons. It's also important to extract the addon using the folder names stored in the Zip archive (an option in your Zip software). This will automatically create additional sub-folders for each addon.
Enabling and Disabling Addons
Right after loading the game and logging into World of Warcraft, you come to the character selection screen. There is a button on the lower left of this screen called "Addons." If you click on this button, it brings up a list of the addons you have installed, and shows you whether or not they're enabled. Newly installed addons are normally enabled by default. You can enable and disable individual addons in this window, as well as re-enable out of date addons, which are often automatically disabled after a major game patch.
When Blizzard releases patches for the game, they frequently affect the way addons work. Sometimes they will continue to function as before, but at other times they will start to cause errors and must be disabled until they are updated. Addons are created by the community and made available for free or by donation, so be patient if your favorite addon isn't updated immediately after every game patch.
An alternative to updating your addons manually is use one of the addon managers offered at some addon sites. These programs make installing addons very simple, and they can update your addons automatically whenever a newer version becomes available. This can be very handy if you use a lot of addons, but there is a slightly higher risk of being infected with a virus.