How Fiction and Nonfiction
are placed on the shelf
are put on the shelf in alphabetical order
eg 826 DAH for a Roald Dahl book
are shelved by their subject's category
eg Cars: 624.6 (You wouldn't worry about the author,
you would just want the facts about cars)
Fiction and non-fiction books are shelved this way so you can easily find the book of your choice.