When we are animating a digital character be it a person, animal or machine we need to use what is referred to a rig which is essentially a control mechanism for that model to allow for movement and control. Similar to an Armature in stop motion (which is a skeletal framework upon which a model is built around) a rig is made up of joints and bones.

These bones are linked together giving structure when linked to points on the model. The model itself is akin to the skin of a person and without the bones correctly linked and attached the model wont animate or move.

We can add weight and constraints to bones and joints to limit rotator movements and apply physics to emulate different environments and conditions.