So just FYI, skinning has a specific meaning in 3D graphics. It has to do with making a mesh follow a set of bones and bend between the bones. I edited your question once I saw your comment that you're really asking about texturing.
You want to know how to texture a complex model. The simple answer is you use a 3D modeling package like Maya or Blender for pretty much anything more complex than a simple cube or sphere. You then need to write (or find) tools to convert the data from the modeling package into something useful for your program.
A few links. Warning: For a complex model it's a complex process
https://blender.stackexchange.com/questions/1022/adding-uv-mapping-to-mesh
https://www.youtube.com/watch?v=f2-FfB9kRmE
http://www.chocofur.com/5-uv-mapping.html
http://sophiehoulden.com/tutorials/blender/unwrapTut.html
There are programmatic ways to apply textures like using various kinds of texture projections. See this answer for a few of them
Almost none of them are very useful except for a few basic things. For example spherical mapping is useful for texture mapping a sphere. But there's really no reason to use a separate spherical mapping calculation for a sphere as you can compute the sphere's texture coordinates as you compute the sphere vertices themselves.