Shaping is the process of creating a new behavior by gradual reinforcement,
starting with an existing behavior, say a dog crouching on all fours.
You then reinforce behaviors that get progressively closer to the behavior you want the animal to perform
in this case you can start by reinforcing your dog rolling to one side..
After reinforcing a particular behavior a few times,
you then require the animal to respond with a behavior that is closer to your desired behavior.
Now the dog must roll onto her back to get reinforced.
Gradually, you require the animal to perform behaviors even closer to the behavior you want,
until the animal finally completes the trick.
This is shaping, defined as the reinforcement of successive approximations toward the target behavior.
Finally, your dog must roll all the way over to be reinforced.