The first concept is based on the fact that the best way to learn something is to teach it. We know that children learn from seeing, listening and hearing. They learn action and attitudes and will copy things that they have seen. So, what is better than using a doll to model the appropriate potty training behavior for your child?
The second concept is based on the fact that behavior is shaped by consequence. As a parent, you already know that children learn from the consequences of their action and you probably have already used this as an effective parenting tool.
There are two types of consequences for action logical and natural. Natural consequence results from the childs own actions. Logical consequence is also a result of behavior, but is imposed by the parent.
So, basically, with your guidance, your child will teach a doll named Potty Scotty or Potty Patty the appropriate "going potty" behaviors. Your child will start learning that the natural consequence of drinking is the urge to urinate. The logical consequence of urinating in a potty are rewards such as such as verbal & non-verbal praise, treats, toys and even a celebration potty party.
Then, your child will teach the doll the natural consequence of not using the potty, which is wet underwear. The logical consequence of this undesired behavior is practicing going back and forth to the potty.
It is as simple as that. And it works.
However, like most things in life, success is a result of preparation and planning. There is no miracle pill it will take some effort and energy on your part to be successful.