While quite a few Mods and AddOns will focus on providing enhancements to specific classes, some are useful no matter which class you play. Click into that to enable, disable, or otherwise adjust your 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. C:\World of Warcraft\_classic_\Interface\AddOns
