Yeah, starting simple is usually the good way to go. 
In general, yes, although you shouldn’t confuse that with the joints between the bones in an Actor’s skeleton. The concept (and hence the name) is similar, but the usage is entirely different.
Still, joints are of more general use. Other analogies would include a hinge, attaching a door to its frame in such way that it can be opened; or a suspension arm, attaching a wheel to the rest of the car in such way that the wheel can move up and down on a bumpy road. Generally, it’s something that binds two bodies together, so they can only move in certain ways relative to each other.
You can read about it in here: opende.sourceforge.net/wiki/inde … anual_(All#Joints_and_constraints .