Animating using Inverse Kinematics
The Inverse Kinematics tool (IK) allows you to pull on your character's extremities, such as the hands and feet, and have the rest of the body follow.
The Inverse Kinematics tool will animate from an extremity and make the rest of the hierarchy follow (called the IK chain). It can be used on any piece connected in a hierarchy. However, you do not have to use IK every time that you have a hierarchy rig. This tool is useful when you want to bend a character's knees, make him sit and move the rest of the body, etc.
Inverse Kinematics helps a new animator to understand how a puppet should move. It will also help any animator easily create difficult moves.
Inverse Kinematics will not work on basic rigs without hierarchy because there is no hierarchy chain present, IK only works on hierarchy parenting when the pivots are properly set.
When animating a hierarchy puppet, an animator will use the Transform and Inverse Kinematics tools.