Weight painting is probably the fastest way to assign bone weights to your model. To enter Weight Paint Mode, just go to the Interaction Mode selector in the 3D View header and select Weight Paint. Now you’ll see the model with blue, yellow, green, and red applied; the colors represent the weights of the currently selected bone. You can also switch to this mode by pressing Ctrl + Tab.
Before you start setting up the bone weights for the model, you may want to change the armature’s display to Stick (in the Display panel, on the Armature tab) so the bones don’t block your view of the mesh; also, only turn on the deformer bones layer.
Weight Paint Mode is very similar to Texture Paint Mode: on the left, you’ll see painting ...