I'm going to disagree about "Lesser key of Solomon", is something you should search up. Lesser Key of Solom has many wrong information about Demons and I've heard the way it shows to summon them..they wouldn't take it very nicely. It is said by many, that Demons hate summoning circles, of any kind, and many people are against using this book's way of summonings.
I may be able to help you into that. You can mail me anytime.
Greetings Amber, May i Ask what you want to learn about them, for you should know there is a lot to learn and understand in the world of Dark Arts which comes to Demonology, Witchcraft, Voodoo and many more? Demonology can go into a lot of paths, so you have to be more specific to what you want?