An electric dog collar can help you to train your dog.  It helps you to give feedback to your dog when they are doing something that they shouldn't.  It can be a very effective method of training your dog at home.

Basically the way it works is that if your dog does something that you would consider to be bad, they you give the dog a small shock through the collar.  Though the shock is not enough to hurt the dog, the idea is that you give the dog an indication that the action that they just did (for example biting you) is wrong with the idea that they will associate pain with it and not do it again.

Sometimes, much like a child, it takes a number of times for this negative reinforcement to set in.  But when it does, the dog knows that certain actions are wrong.

You need to make sure that you also use positive reinforcement as well such as giving your puppy treats when they do something good.  This will teach the dog the difference between doing something good and bad and will help greatly with your training.