American Bulldog puppies grow into powerful adults, and although they're generally good natured they can be suspicious of strangers and have a guardian breed type attitude.
It's important to begin basic training early and to continue it throughout the dogs lifetime. As soon as he's had all his shots I'd recommend that you enroll him in a Puppy Class. It's also very important to give him lots of socialization experiences so that he learns to be comfortable around lots of different people and places.
Always be sure to make training sessions fun for your puppy. Use lots of positive rewards and encouragement. Although he'll be a big dog, your puppy doesn't need (and won't respond well to) harsh or negative training methods. In large, self confident dogs, a raised voice or unnecessarily harsh treatment will often cause problems rather than solve them.
You can find tips and advice, and learn about basic puppy training at this url http://www.the-puppy-dog-place.com/puppy-training.html and see a selection of recommended dog training books here http://www.the-puppy-dog-place.co/dog-training-books.html