To understand how to start your newfoundland training, you need to also understand the history of these dogs and realise what they were bred for.
Newfoundlands, like almost every giant breed, were bred to work independently of humans. They have been used in the past for many things, including pulling carts, but their main function has always been rescue.
This inherent breeding makes them good pets, as they are naturally people friendly, but you have to remember that they will act on their own initiative if they think someone is in danger.
This independence means that they think of themselves as equals. They will not respond to harsh treatment; indeed such treatment can destroy their trust in you permanently. They will not respond to any outdated pack leader theories either. You are not his pack leader, he does not have a pack, you are his friend and the controller of all his resources.
The independent nature of the newfoundland dog gives him an edge in intelligence, but he will not work for free. Positive, reward based training is essential. If you want him to do something for you, he wants to know what is in it for him.
If you have an older newfie who has perhaps missed out on his basic puppy training it is not too late, though it will take much longer and will require more patience.
Find a high value treat that your newfie loves. Most newfies will do anything for food, and by a high value treat I mean something that he does not get all the time. He is not going to co-operate for a boring old dog biscuit!
You will need something different, pieces of chicken, pieces of cooked liver - many dogs love cheese, which is fine so long as it is given only as a treat and in small quantities. My dogs will do anything for liver cake.
You will never force a newfie to do anything. They are easily frightened and they may never get over that fear. You do not work for no wages, why should he?
A nice high value treat, the second he does what you want, will get him interested and looking forward to the next command.
You need to build a relationship with your newfie so that he will do anything to please you. None of this is difficult, but it does take time and patience, especially if he has had no training. If you adopt a newfoundland dog from Newfoundland Rescue it is likely that you will have to start from scratch.