Chokers are supposed to pinch the skin. I was told that you're suppose to say a word like, "no", or "don't pull" (or whatever), and then jerk the leash and this will pinch the skin. So, whenever the dog pulls and you say "no", he'll realize, "hey, i think something painful is coming, i'll stop." Something like that.
However, when I used it, I found that Levi just kept pulling and pulling and after a few months, his neck was really pinkish/red, so I stopped using it. I then bought a halti and found it to be my miracle.
You could also try just teaching him not to pull by going for a walk and whenever he trys to pull, stop. Just completely stop in place. Then gently pull the leash back to you and say "near". When he's next to you, give him a treat and continue to walk. You'll end up stopping A LOT, but after awhile they start to get the hint that "near" means to stay next to you and when they pull, they don't get anywhere.