Torsion bars in trucks help absorb impact. They are fixed to the body of a vehicle at a set height on one end, but twist, yield and return to a straight rod based on the movement of a control arm that levers up and down. This vertical arm attaches to the torsion bar by movable bolts. Tightening these bolts manually or with tools such as torsion keys can raise the bar and make a car or truck sit higher.
Picturing this setup is a little challenging due to the name "torsion bar." Though the torsion is absorbed through the bar, it's not actually horizontal rod moving up and down. It's more like when you're squeezing water out of a towel. Twisting the towel tightens it up and releases the absorbed water, while untwisting the towel loosens it up and makes it shaky. A torsion bar twists and acts as a spring to absorb the vertical force of the arm, and when the bar is tight, it's more rigid and creates a harder impact for the vehicle. If the torsion bar is too loose -- like the unfolded towel -- it holds too little of the spring and the car's handling becomes wobbly.
Lifting a vehicle with a few turns of the torsion bar is simple and quick, but getting the height balanced is key to maintaining the handling. Investing in torsion keys or kit systems in the $100 to $200 range is a good option to ensure a level lift.