A slide hammer isn't really a hammer; it's a tool for violently pulling something with a single easy motion. The tool is used primarily for auto body repair and other in situ sheet metal work to pull out dents.

The device is made from a long steel rod with a replaceable hook or screw-tip on one end and a handle on the other, with a steel ring welded to the rod at the handle end. A heavy metal cylinder (the slide hammer), usually flared at the ends and scalloped for a better grip, rides the rod between the hook end and the handle. It looks strangely like a meter-long hypodermic for a robot.

In use, you hold on to the handle end and screw or hook the other end of the slide hammer into a hole (either existing or created) in the dent. Then, bracing yourself, take the slide in your free hand and whip it towards the handle. When the weight hits the handle, the force pulls out that part of the dent (this doesn't take a great effort, the weight does all the work.) You have to be controlled in your pull, because if you pull too hard, you may rip a bigger hole in the metal, and if you pull too softly, you may not do much to the dent. Once you have the metal relatively level, fill in the holes with bondo and paint.

Another, nefarious, use for a slide hammer is to snatch locks. In this application, one would screw the slide hammer into the keyhole of the lock, then slide the weight as hard and fast as possible, as the object here is to rip out the lock cylinder. Unless the lock has a metal plate covering the cylinder (a fixture in New York apartments (and some cars) along with the anti-pry steel strip on the doorjamb), the lock will be defeated. (Note: Do not try this. It is illegal.)