Choke collars (also called slip collars or choke chains) consist of a length of chain with a ring at each end.  When you attach a leash to the dead ring, the collar does not tighten on the dog's neck.  When you attach a leash to the live ring, the chain adjusts more tightly when you pull on it and loosens again once the tension is released. A gentle tug with immediate release, called a "correction or "leash pop" is used to teach your dog that he has done something undesirable. 

The use of choke collars is somewhat controversial.  Some trainers will tell you they can be a useful tool in training, while others are adamant about not using them.   All ten professional trainers in a recent survey agreed that this type of collar should only be used by experienced handlers while seven of the ten agreed it might be a good idea to include a warning label on the collars at point of sale, as there have been incidences where the collars have "locked".   

The name choke collar can be a bit deceiving, since correct use of these training devices does not involve choking the dog.  That being said, it is important to be aware that improper use of this type of collar can result in injury and the choking death of a dog. 

Ultimately, the use of a choke collar is something you will need to decide for yourself.