A skeleton is an object that has joints
and bones.
Pose a skeleton by moving the joints. As you move a joint,
bones hold the skeleton together (using inverse kinematics, or IK).
Objects can be attached to the bones, so that the bones control the objects. You can control an entire figure by attaching objects to bones.
The process of setting up a skeleton and attaching objects to bones is called rigging.
Skeletons have special properties for selection and keyframing. See these sections: Selecting, Keyframing, Menus.
A Motion Studio skeleton is really a trueSpace group. The group is set up as shown here:
The BoneBag is a group object inside the skeleton which contains the actual bone, joint, and other helper objects that comprise the skeleton. Most of the time you will not need to open the BoneBag. Generally, the joints and bones are selected instead with the Skeleton List or by clicking in the trueSpace interface.
The Body object in the example above is an trueSpace object that has been attached to a bone. Attached objects are automatically moved into the skeleton group by Motion Studio.
The PartsGoHere object is just a placeholder: all trueSpace groups must have at least two children. An empty skeleton has only the BoneBag as a child, so the PartsGoHere object is created to keep the group together. The PartsGoHere object can be deleted after you have attached some objects, but it's recommended to leave it be, to ensure that the skeleton group does not get lost.