Mathers' "The Book of Goetia of Solomon the King" Aleister Crowley wrote some solid essays that kind of make sense in it. But in general most books on demonology are going to be hard to understand, and like wise were written by people who were quite mad. I.e. Crowley, who is a piece of work. To the person who asked, find different translations of it, usually can piece together what you truly need. But be careful. That sort of stuff is all about summoning the worst.