Ok, follow these easy steps to skins working
1. Download the skin and save it anywhere as long as you remember where you put it
2. Open up World Editor (WE) and load up your map
3. Go to import manager (the top buttons)
4. Import the skin with it (find the skin and add it)
5. Double click/right click to add the path. The path is basically is a sensetive sequence of text which is followed from your war3's mpq archive
6. The page you downloaded the skin should include the path for the skin, if not, ask me now
7. The skin now works in the game. You don't have to do anything now because its automatically applied itself to the model
GL!!