Book

Books are items used in enchanting.

Bookshelves
Three books are dropped when a bookshelf is mined without silk touch or destroyed by an explosion.

Enchanting
Books can be made into enchanted books by enchanting them on enchantment tables.

Trading
Librarian villagers will usually buy 8-10 books for an emerald.

Librarian villagers buy 4 books for an emerald as part of their second tier trades.