A torsion bar is a solid bar of spring steel which is connected to the car chassis at one end, and free to move with the suspension at the other end. The spring action is provided by the steel bar's resistance to twisting. On Rangers, there is a short arm at the rear of the bar with an adjuster bolt that allows height to be corrected or changed.
This is a generic torsion bar set-up. It is not a picture of a Ranger but it is similar in principle. The torsion bar is keyed to the lower control arm of the suspension.