Satanism as represented in the satanic bible is LaVey Satanism.
They do not view Satan as a demon but as an archetype for the inherent greed in humanity.
So, Satanism is more or less 'worshipping yourself', put incredibly roughly. From my understanding, it's more a philosophy than what is usually thought of as a 'religion'.
I have limited knowledge, stemming primarily from Wikipedia and my brother who considers himself a Satanist.
Research, I say. ^^