The basis of everything seems to be in demons.
Demons have two forms.
Manifestation: Fully summoned into the real world, takes a circle and a ritual, time and privacy. Manifestation is required to first make contact and make deals.
Spiritulization: You can after making an agreement summon a demon only as an incorporeal being, technically it's is allowing part of them to possess you temporarily. This works best with a steady arrangement with minor demons and is normally used to call upon their powers.
Manifestation requires a circle: Circles are barriers between this world and hell, allowing you to stay safe (relatively). The strength of a circle is based upon your will power, and the quality of the circle, physical ones work better than drawn ones. Ones with sacrifice in some manner built in work best through. One made with bones would be incredibly strong, but would be destroyed after use. One made of steel would be weaker but be reusable.
A common tactic is to draw the circle in your blood if you don't fuck up it's strong, but if you do they now have your blood. (This is bad)
Types of demons:
The lowest ranking demons are called imps, and for now that is all I am studying.
Imps: Obsessive, Imps are tightly bound to their nature, and will do anything no matter how short sighted to further that idea. A rage imp will murder the closest thing if let free. However a stronger demon of rage, would probably become a terrible serial killer or try to start a war even.
---[] Lust Imp: One of the most dangerous, the focus on the carnal and manipulation through desire. If you have a virgin to sacrifice though they can be quite willing to work with you.
---[] Rage Imp: A simple imp, think of it much like an attack dog, you can probably make it agree not to attack you as long as you are throwing it into people to hurt.
---[] Dead speaker Imp: Those who are in contact with the dead, and can carry messages for a price, one of the most diverse imprs
---[] Forbidden knowledge Imp: An imp who cares only for spreading Diabolism, probably because it normally ends badly for the diabolist. Likely to work with you cheaply, but will want you to teach others in time.