For me, shaman is somebody, or something, that comes from "inside" (from the depths of ones being) and becomes you. You are not possessed, you simply are a different being for awhile. The difference in you, before and after, is obvious. Wisdom is deep, ability to solve problems profound. The perception of reality is different. There is no "magic", since every solution comes through understanding. It's a state that could be easily called omniscience.
I am not a shaman currently, but I've been one few times. I was able to heal myself physically, and others mentally, to some extend.
Unfortunately, I don't know all the conditions that are necessary for it to appear. Not yet. What I know for sure, it that "it" is interested mostly in daily life, present moment, ones surrounding and social relations. "It" wont tell you how to become a milliner, but "it" is able to solve all your emotional problems.
It is real.