Regardless of whether you walk your dog on a flat collar, a martingale, a slip leash* or a prong collar* (note: I do not list ”harness” here as they were designed to pull and will make most dogs pull), any dog must first learn what the leash means. The principle remains the same for all the aforementioned tools.
Our dogs must learn the concept of “pressure-release”, basically wherever the leash goes, the dog is to follow. To teach them this, apply a little pressure to the leash (with a small tug at the leash) and as soon as the dog gives in to the pressure, release.
Similarly, we teach the dog when we stop, the dog is to stop. For this, we pull up the leash gently with a little pressure, then release as soon as the dog stops.
The ultimate goal is for the dog to learn that pulling does not pay, i.e., is not rewarded: they do not get to move forward. A behaviour that is not rewarded, will eventually be extinguished. Not pulling on the leash is what keeps them moving forward. A behaviour that is rewarded, is more likely to be repeated. Remember: Behaviours are reward-driven.
*I strongly advise pet parents to consult a qualified trainer before using these training tools. Used correctly they can be safe and effective, however, without knowing how to use them correctly they can be dangerous and may result in serious injury.