How to Install AddOns
Once you’ve downloaded an AddOn or Mod, you’ll need to locate the “AddOns” folder on your computer. This will be located on whichever drive you used to install WoW Classic. The path will probably look something like this:
C:\World of Warcraft\_classic_\Interface\AddOns
Simply paste the downloaded (and unzipped) AddOn file into this folder, then boot up the game, and you should see an “AddOn” option on the character selection screen. Click into that to enable, disable, or otherwise adjust your AddOns.