Week 6 Skinning

To make the mesh follow the bones or biped a skin modifier must be attached to all parts of the skin.
Furthermore within the skin modifier the bones which will be controlling the bones have to be chosen so the modifier knows where each bone is connected with the mesh.

Skin Modifier Add Bones:

To adjust the vertices so that they follow the bones in a way that the "skin" mesh looks natural envelopes have to be adjusted for each bone or vertices.

I do prefer vertices manipulation as the rigger has got more control over the weights.
A weight table and vertices weights help to adjust them to fit the skeleton.

Here is a simple tutorial about rigging and skinning (using envelopes)
http://www.polygonblog.com/character-rigging