I suppose the word itself can refer to multiple things.
There is theistic Satanism, where the practitioner believes Satan is an extant supernatural entity to be worshipped. I am not well versed on this matter, but I suspect that given its unpopularity (for obvious reasons), it must be a mostly personal religion, or one for only very small-scale congregations. With that in mind, it must be highly variable depending on the individual or congregation.
There is also LaVeyan Satanism, a philosophy pioneered by Anton LaVey. Interesting enough, LaVeyan Satanists generally don't believe Satan is a literal, supernatural entity, and instead revere him as a symbol of their ideals, something to strive for. There's a joke that LaVeyan Satanists are just atheists who really like Halloween. Anyway, chief among their core values is personal responsibility. If something is wrong in your life, don't whine about it, make it better, so say the LaVeyan Satanists. I also know that they consider pretensiousness and willful ignorance to be sins.
In either case, I think it's a bit silly. Granted, I find I even mostly agree with the LaVeyan's philosophy, but I just think that anybody who proclaims to worship or revere Satan is just trying to horrify the Christians and draw attention to themselves. As I said, I can even agree with the LaVeyan's much of the time, but it's not at all necessary to have Satan for a role model.
For a long time of the word's existence, there weren't really Satanists. People just want you to think anyone different was certainly worshipping the devil. However there are modern day LaVeyan Satanism which is more rooted in self determinism and independence rather than relying on an higher power or believing in karmatic justice.
The other funny one is "beelzebub" , which is a mix of the word "Baal", whom was a god to the ancient Phoenicians, and "zebul" which meant "dung". So beelzebub is just an old term the Hebrews came up with to make fun of the Phoenicians deity!
Both are ways for teenagers to be exceptionally rebellious if they hate their parents more than the regular amount. Or for adults, it's either when those same teenagers never got over it, or have an extra dose of schizophrenia.
You need to specify as there are some sub groups. The people that are too romantic and dig angels and flowers and happiness, the heavy metal fetishists, the counter culture.. I, myself am Laveyan, the only group that can defend their philosophy rationally, and that I've found incredibly compelling. what you heard about that already is correct, but I'm here for questions if you have any, oh and the reason striped power is pissed off at them is that I cut at his believes with ockhams razor previously, just a btw. ^^