My dogs in the past have just learned over time. I'm finding it hard with my puppy right now, because she hates going out in the cold. When I carry her out, she goes 100% of the time outside, but I have to chase her down to pick her up. Maybe as the weather improves, puppies will be more independent in wantint "outside" I think once she gets this, I will try the bell. Our vet said that in order to do this, owners ring the bell, along with stating "out" or "outside" as they're opening the door. Eventually, they catch on.