When you are training for a job, you wouldn't take to well to someone yelling at you or hitting you for not doing the task you were given correctly would you? Probably not. Dogs are the same way. They are very sensitive to the vibes we put off. They can read our every emotion.
When dogs are learning new commands, they are trying to figure out what is right and wrong. Rewarding your dog for completing the command builds a healthier relationship between you and him. You can reward your dog by giving him a scratch on the head, a treat, or a verbal praise. Doing this, will let him know that what he is trying to do is correct. He will realize if he does the command, he will be rewarded. Doing this makes a much easier process when training your dog.