Weight Painting

Weight painting is used after you have bound the skin to the skeleton. With this tool you can affect the way that influence that each joint has over the skin and the way it moves. You can use it to make the movement of the skin look more realistic.

After selecting the mesh double click on the paintbrush icon shown in the picture above to open the weight painting menu shown on the left. 

Here you can select each joint in the list and it will show you how much influence each joint has. The more bright white an area the greater that joint has influence over the mesh. 

You can add paint by selecting add as shown above simply paint onto the mesh. You can smooth the paint so that it has less of a harsh start and finish and is more blended by selecting smooth or simply holding down the shift key as you paint. You can also change the strength of the brush in this menu.

In order to see how the painting is effecting the rig you can move it up and down, but an easier way to see without having to switch to the move tool is to set up a couple of key frames to make the leg bend so that while in weight painting mode you can simply move the slider  at the bottom of the window and the leg will move up and down.