To use skins
You must first import the skin, by clincking useing the built in tool in World editor.
Now if you are trying to use skins from a model you have downloaded from this stsite simply look at the,
"Number of Skins:" information.
It will give you the path as
skinname.blp
or
something/skinname.blp
or
something/something/skinname.blp
in the importer change the path of the imported skin by double clicking it and hitting custom path too,
the provided
skinname.blp
or
something/skinname.blp
or
something/something/skinname.blp
now if your trying to import over an exsisting model in wc3 like arthas you would use that models call for its skin, so...
ill get the list of paths but for now use wc3 image viewer and open the model you want and click show paths.