Satanism is a very broad term. Meaning that there can be many types of satanist. But One of the main things is admire satan. Some are satanists because they like evil things and whatnot, but some believe that satan/lucifer is the good guy with a bad reputation.
After note: You might say satanism is like members of this website. All the people with different views, motives, and beliefs, but they are all(most) striving to find what they believe in, what they think is the right path. I hope this helps.---Sazar
Satanism is a broad and diverse group of practices, beliefs, religions, and theologies.
Most satanists are either non-theistic (agnostic or athiest, using the symbol of Satan/Lucifer/baphoment as a symbol to be admired. They may be satirical in nature, but not always) or theistic (actually believing in the supernatural, possibly worshiping or revering satan/lucifer/etc).
Both of these two types can further be broken into various theologies and beliefs.