How to use joints to create a skeleton that can be used to deform an object. This is a simple fish demonstration and does not go into the full IK setup needed for a complex character, but I would highly recommend starting with something simple like this before trying to rig a character.

The Paint Weighting is shown briefly, but that is the major area of focus in a complex rig and can take much longer than modeling of designing an IK rig. For our purposes, we will only be learning simple rigs and not get into the complexity of full-blown character animation rigging.

If you are following the Step by Step tutorial, here are the steps in order:
Polygon Modeling
Joints
Cloner Object – Introduction
Cloner Object – Using Object Mode to animate
Target Effector
Optimizing Mograph Cloner for Display speed
Random Effector
Timeline
FCurve Offset to Delay Loop start
Specular and Diffuse Maps
Transparency Absorption
Refining Lights and Visible Volumetric settings