The BodyForce object applies (or exerts) a force on the part to which it is parented. If the magnitude of such a force is great enough, parts can begin to accelerate. The force is determined by the BodyForce.Force property, and is defined on the three world axes.
A BodyForce alone cannot apply a torque (it cannot cause the parent to rotate on its own). To apply a force at a specific point (e.g. to apply torque for angular acceleration) or apply forces relative to the orientation of the part, use a BodyThrust instead.