Typical positive reinforcement events will satisfy some physiological or psychological need, so it can be food, a game, or a demonstration of affection. Different dogs will find different things reinforcing. Negative reinforcement occurs when a dog discovers that a particular response ends the presentation of an aversive stimulus. An aversive is anything that the dog does not like, such as verbal admonishment, or a tightened choke chain.
A training class is not there to train your dog. Its purpose is to teach you to train your dog so you will need to be committed to train your dog for short sessions (5 minutes) several times a day rather than just simply turn up for classes! This little bit of training everyday will be repaid with a lifetime of living with a well behaved dog. You will also learn to avoid problems before they begin as well as receive help to overcome any that you already have with your dog.