The book is for enchanting items on the anvil.
To make an anvil you need 31 iron ingots. In a crafting table grid, place 3 blocks of iron across the top, 3 iron ingots across the bottom, and an iron ingot in the center:
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Then place the anvil, use it, place an item in the first slot, the book in the other. The enchantment costs Experience levels too (and you gain these gathering experience spheres by killing monsters, mining minerals, and smelting items.)
For example, a book of Sharpness III used on iron sword will make the sword cause 1.5 heart more damage on each hit.
You can enchant normal books too, using enchanting table - which might seem useless since the resulting book will have only one enchantment and you'll have to pay the exp cost twice (first, creating the book, and then again, enchanting the item with the book on the anvil). The serious advantage though is that the enchanting table gives enchantments randomly while the book gives the item exactly the enchantment of the book.
Imagine you want to make your diamond boots to have featherfalling enchantment. You can waste 40 diamonds on enchanting one pair of boots after another on the altar until you finally get the featherfalling - or you can use up a bunch of leather and paper until you get a book of featherfalling, then just apply it to a single pair of boots - 4 diamonds total.
/xp -5000000L mikeTheLiar
The xp command does not work with negative experience points, but works for negative levels, according to the Minecraft Wiki.
Best Answer
No, you can't combine the poison with stuff at the moment, but it might be a planned feature.
But you can create a splash potion out of your poison potion. Because you can throw a splash potion it can be used against other entities. Just beware, skeletons and zombies don't take damage from them. To kill these you need a splash health potion. Source