Satanism is not one single religion. Satanism is a broad category of religions, worldviews, and literature all featuring a favorable interpretation of Satan. Christians (and Muslims) regard their God as all-good and Satan as evil. But what is good? What is evil? Many of the moral values espoused in the Bible seem very strange from a modern Western point of view. In the Garden of Eden story, Adam and Eve are punished for eating from the "tree of knowledge of good and evil." In other words, blind obedience to the Biblical God is considered "good," whereas independent moral judgment, based on one's own knowledge, is considered "evil." But, like many other educated people in the West today, Satanists do not agree with this idea at all. In the Book of Genesis, "God" seems to be outright threatened by human knowledge and achievement, both in the Garden of Eden story ("And the LORD God said, 'The man has now become like one of us, knowing good and evil. He must not be allowed to reach out his hand and take also from the tree of life and eat, and live forever.'" - Genesis 3:22) and then later in the Tower of Babel story ("But the LORD came down to see the city and the tower that the men were building. The LORD said, 'If as one people speaking the same language they have begun to do this, then nothing they plan to do will be impossible for them. Come, let us go down and confuse their language so they will not understand each other.'" - Genesis 11:5-7).
According to traditional Christian doctrine, the main “evil” thing Satan is believed to do is simply to lead people away from Christ. Whether this is a good thing or a bad thing depends on how you feel about Christianity. From a more down-to-Earth point of view, the worst thing Satan is said to do in the New Testament is to drive people insane. (Insanity is blamed on alleged “demon possession.”) Indeed, if one is careless, one can drive oneself insane through exploring the unknown and seeking to “become as gods,” as Satan invites people to do. On the other hand, if one takes reasonable precautions in pursuing one's explorations and ambitions, one can reap great benefits. Thus, most Satanists do NOT see themselves as "worshiping evil." Rather, most Satanists associate Satan with such values as pride, independence, individuality, knowledge, achievement, thinking for oneself, and exploring unknown and forbidden realms. Furthermore, contrary to the portrayal of Satanism in horror movies and sensationalistic tabloids, the vast majority of Satanists do NOT see any need to sacrifice animals or commit violent crimes in the name of Satan. There are many kinds of Satanists. For most of the past forty years, the most public Satanist spokespeople have been atheistic symbolic Satanists, who do not believe in or worship Satan as a literal entity, but who regard Satan as a symbol of independence, pride, individual ambition, etc.