Most dogs do it naturally.
I sincerely hope you aren't thinking of training her to guard.
I'm sorry to sound mean, but since you have very little knowledge about dogs, you have no business training a dog to seriously defend your or her territory. A dog trained in protection takes a knowledeable handler, someone who knows how to control a dog and someone who understands dogs, and from your previous posts I'm convinced that you are not such a handler.
Almost all dogs have a natural territorial instinct, and since she is still a young dog, that instinct probably hasn't kicked in yet.
Renee gave a good recommendation, the Monks of New Skete books & videos are great, they should teach you what you need to know.