The most famous one has to be the one you're thinking of. Believing, and devoting yourself to Beelzebub, the ruler of hell. Sacrificing animals to gain Satan's sympathy or power. The literal sense of Satanism.
However, there's another that's completely different. It is called LaVeyan Satanism. These type of Satanists don't believe in any gods, nor do they believe the devil known as Lucifer. They state Satan as a symbol of Man's true carnal, and ruthless nature. They support in taking vengeance on someone who has done you wrong, aka the dark emotions of man.