In reply to the9thresident:
I'm not sure if you're using any kind of addon manager, the manual way is as follows:
0. Stop World of Warcraft Classic if it's running.
1. Delete any existing folder named Skinner in the 'World of Warcraft > _classic_ > Interface > AddOns' directory.
2. Download the latest file from this page.
3. Decompress the downloaded zip file.
4. Move the Skinner folder created in step 3 into the 'World of Warcraft > _classic_ > Interface > AddOns' directory.
5. Start World of Warcraft Classic, click the AddOns button in the BLHC of the Character Select screen, and check that Skinner appears in the displayed list.