Steel springing will normally take one of three forms; leaf, coil or torsion bar. The leaf spring has been fitted to many vehicle types over many, many years and has the advantage of being able to locate, an axle for example, without much in the way of extra linkages.
The coil spring, which is probably the most common form of car/light commercial springing, has no such advantage requiring turrets, linkages and platforms for accurate location but it does have the very useful attribute of being compact and therefore easier to incorporate into the modern vehicle design.
The less common torsion bar is quite simply a square or round section bar fixed at one end to the suspension arm (moveable) and the other to the structure/bodywork (fixed). The operation of each of the above as a result of impact is for the leaf spring to deflect whilst increasing in length, the coil will simply compress and the torsion bar will absorb the movement by twisting about its length.