Satanism, depending on the tradition the Satanist is involved in, comes in many forms. Some Satanists believe Satanism is the worship of Satan as a deity while others believe he is an entity, a being, a force of nature, or a symbol representing freedom and indulgence. Although there is controversy as to who is right and who is wrong, I think it is up to the individual.
To me Satanism is believing in yourself. If you didn't believe in yourself than nothing else would matter. Satanism wouldn't be as effective without the self belief of the individual and would be just an empty shell with no meaning. To me he is not only a force of nature, or a reservoir of power that each and every one of us has within that we can tap into at will, but he is also a symbol that I choose to wear around my neck. He is also a symbol of man's pride.
But the bottom line is this: Satanism is about YOU and finding the path that is right for you.