Satan by definition, it's true definition, is The Advesary, or the opposition. We oppose the Satus quo, and the herd mentality. Instead we ebrace Intellect, Objectivism, Individualiuty, and Rational self interest.
You are the only person who has control over your life, no "God" will make your life better for you. It is much like Santa Claus, we are told as children that if you don't believe in him you will be punished by not getting any presents. Religions of all kinds work in much the same way, with the exception of Satanism. We do not believe in things we cannot see, and yes that includes "Satan". Why should we, that is not rational.
I'm sure you are asking yourself, "Then why the name Satanism?" The answer is quite simple. Throughout history all religions have only preached obedience and faith while Individuality, and rational thought has been condemed. It wasn't that long ago that the Churches attempted to ban books that provoke thought, and make people think for themselves instead of buying into the church scams and guilt trips. Satanism is quite the opposite, hence the term "Advesary" (The definition of Satan)