What can my magic system actually do?

In my story idea, magic is pulled from Chaar, the fallen realm that used to be heaven before god was killed. I have the idea that the channeling magic from this place will eventually drive any mortal mad as it is the power of the divine. Unfortunately that is as far developed as I have it and I am having a hard time figuring out what magical abilities magic users would actually posses. I’ve never made a fleshed out magic system before so I’m a little lost for direction.