What does a martingale dog training collar do?

I have only just heard about them and was interested to know if they help to train a dog to walk on a lead properly without pulling or barking. Thanks if you can help.
Well she is just a small dog that I got from a shelter who has never learnt to walk properly. I’ve tried the other harnesses that go over the nose and under the body but they just cause her to have skin irritations so I stopped using them. I’m at a loss to know what to do with her. Any ideas would be appreciated.

Need help with Fitting and using a martingale dog training collar!?

I have a martingale dog training collar for my dog, I got the right size and all, but I am not sure where it is to sit on the dogs neck and that kind of stuff so any help would be appreciated.
the martingale dog raining collar I got has the partial chain on it, so does it matter where that DRing is for the leash to go on? Oike am I pulling to the side or straig twards me if the dog is on my left?