Essentially Satanism is the worship of the self. Anton LaVey coined the term "Satanism" simply to draw a line in the sand, so to speak, between what he was writing about, and the beliefs of christians. He was promoting something that wasn't quite Atheism, because he did believe something, but it also wasn't Agnostism, because that is simply backing away from any belief.
Basically he had read a great deal about Humanism which places the individual above that of the society and places responsibiltiy on the individual for their needs and for the consequences of their actions, rather then a Deity. But LaVey wanted to take it a step further. He was a bit more proactive then the Humanists, and Humanism was also a Lighter version of Satanism. While Humanism does promote putting the self first, it is more passive about it. Satanism is much more aggressive. A Satanist believes that you need to go after what you want and looks down on laziness.
Satanists have a sense of honor, but it is all based on self needs. So it comes across as selfishness, although they would never use you or expect you to do things for them. They do for themselves, and expect you to do the same for yourself.
They also truly worship themselves. In a dark sort of way, this is their way to good self esteem. By "worshipping" themselves, they are learning to love themselves. Whereas a Humanist (who is more gentle and passive) might meditate to relax, a Satanist would indulge in things they enjoy. Be it drinking, food, sex, whatever. So long as their indulgences never infringe on anothers rights. All religions have at least one Creed or Motto and Satanism is no exception. Their main Creed is "Your rights end where another's rights begin". So they do whatever they want, but will stop short of infringing on someone else's rights.
The main reason for the word Satan, is that there really is no other word to be used to indicate yourself. How do you say I am a Me-ist? And to LaVey, Satan represented self indulgence, free thinking, control over your own life, and many of the things that Satanists believe. THAT is why they call themselves Satanists. Simply because the things that supposedly the figure of Satan represents (as mentioned before) are the things that Satanists pursue. It just so happens to be one of those religions that is so wrapped up in stereotypes that many do not understand it.
I am not a Satanist, but I was one for a year or two. I learned a great deal from the experience and respect anyones choice of what path to follow. I only look down on those who insult something without knowing anything about it. which is something that I picked up from my time as a Satanist. ;o)