Spellbooks?

How I can use the spellbook? What is its purpose?

spellbooks teach monsters moves they otherwise may not learn. however certain monsters cannot learn certain moves: any monster can learn books from beginner chests, aka the basic beginner moves, rare, epic, and legendary monsters all can learn intermediate moves, aka ones from intermediate book chests, while only epic and legendries can learn the advanced ones. in addition elemental types play a big role, as only normal, psychic, and ghosts can learn any elemental type move, and normal, psychic, and ghost type moves can be taught to any monster using the above uncommon, common, rare, epic, and legendary restrictions, for example a crusty is rare and can learn the psychic move mind game but not a more advanced psychic move such as mind bending