I have my first inside dog. Any advice on house training?

Answers:
My parents just got a puppy in July and they hung bells on the doornob at the backdoor, and rang them everytime they took the dog out, now she rings the bells when she has to go outside. They always take her out the same door and always praise the dog for going outside. They say that if the dog goes in the house, immediately take the dog outside, do not put it's face in the mess, they don't understan.

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what kind of dog?? age of dog?? and why is it an inside dog?? dogs need to go outside for bathroom, play and exercise.