Books can transmit knowledge in at least two ways. First, there is the literal or factual knowledge which can be gained by reading non-fiction books. For example, if you were to read a cookbook or a biography, you would be learning real, factual information. Books can also give us knowledge through the experience of reading. Many people feel that when they read a book, especially works of fiction, they interact with "another world." Reading books gives us the opportunity to learn through vicarious experience. Even if the story we are reading is entirely fictional, like the Lord of the Rings series, we gain emotional knowledge through the experiences of the characters. Consider someone who has never had a friend or relative pass away, and may come to know grief through the death of a favorite character. Though it is not factual knowledge, it is experiential and emotional knowledge.
Our experiences with books also offer us more implicit knowledge about what books are. By handling and reading books, we come to know that they are typically made of paper, but may also be made of leather or vellum or even plastic! We learn that books may be printed, hand-written, or contain no words at all. The experience of a book is just as much a way of learning as it is to read the words inside.