A slide hammer is a tool with a long round shaft on which a hammer weight slides. The force produced by moving the weight quickly toward the end of the shaft is used for pulling out dents in auto body repair work or for loosening or pulling off tight parts. The name "hammer" is a bit misleading since this is a tool used not for striking but for violently pulling something with a single easy motion.
A slide hammer 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, travels along the rod between the hook end and the handle.
To use a slide hammer for pulling out a dent, hold on to the handle end and screw or hook the other end of the slide hammer into an existing or created hole 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. The pull must be controlled in your pull, otherwise it may tear a bigger hole in the metal.
A slide hammer is often used in combination with a panel puller.