Okay! There we go:



You have to create a mapping and import a picture for the skin.

What you've got is a 3D Mesh of your model, what you still need is a 2D mesh of your model.

Experiment with this 3 functions:
Create 2-sided Mapping
Create 6-sided Mapping
Create Atlas Mapping

Try the first first, then click Edit > Skin Editor and look what you've got there. That's a very basic layout of your model's mesh.
Just to get the principle, import in the skin editor a pic, and look at the model in the 3d view, to see how the pic and the 2d layout of the mesh results in the skin on the 3d mesh...