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Select the enchantment table recipe, or combine the items as follows on the PC advanced crafting system:  Top row: empty, book, empty Middle row: diamond, obsidian, diamond Bottom row: obsidian, obsidian, obsidian Place the enchantment table somewhere with at least two blocks of space on three sides, in a room at least two blocks high. This gives you the space to improve it with bookshelves, as described below. Nearby bookshelves unlock more powerful enchantments from your enchantment table. To make a bookshelf, place three books in the center row, then fill the rest of the grid with planks. These more powerful enchantments will also cost more experience. You may want to skip this step if you're low level. To get the best enchantments, you'll need fifteen bookshelves. Each one must be placed as follows:  On the same level as the table, or exactly one block above it. Keep exactly one empty block between the table and the shelf. Even torches or snow will stop the effect.

Summary:
Craft an enchantment table. Place the enchantment table. Craft bookshelves (optional). Place the bookshelves.