Skinning is the process of binding the character rig to the polygon mesh to be driven. The process starts with the association of the joints to drive the deformations of the mesh vertices. Unfortunately, the process doesn’t stop there. Typically, you will need to adjust the amount of energy imparted to each mesh vertex from the driving joint’s influence. This is done via weight painting. Weight painting is a necessary, though sometimes painful, part of the skinning process. Without it, you will see some really bad joint deformations, among other artifacts.
The idea behind skinning is to have smooth transitions from one joint’s area of influence to another. You can see the energy display projected onto the skinned mesh when selecting a skinned joint; it will appear in one or more colors, blended together. As you move the associated joint controller, you will see whether or not the level so transition is acceptable. If not, you will need to blend more, or adjust joint weights, etc.