The spell book is a useful item to have, allowing mages to organize their spells and save space at the same time. The spell book, when equipped, can be scrolled through either by pressing and rolling the mouse wheel. Spell books can be dyed a variety of different colors. They can also be enchanted with Soulbound. (Not quite sure what else)
When you have the Spell book in your hand, press Shift and Right click to
open the spell book interface. By default, the Z and X keys cycle through the available spells in the leftmost column. In addition, one can scroll through the left column
Arcane Spell BookEdit
This is the same as a normal spell book, but it slightly buffs damage and reduces mana cost for all spells stored inside of it. It rarely drops from the Arcane Guardian.
There is a fairly common glitch where you will be unable to scroll through your spells, especially with Z and X, as it automatically crashes your instance of Minecraft. Be wary. This is also an issue with the Arcane Spell Book.