Some believe the "Satan" was a name given to a much older god. The one that actually did create life. Xianity plagiarized much older religions, forced others to convert or die, then destroyed the evidence of the occult knowledge given to man by Satan, or Lucifer. This knowledge was to help mankind elevate themselves spiritually to the point of being gods themselves.
There are some Satanists who don't believe in any of sort of deity at all. They usually follow the works of Lavey and are basically atheistic in their belief system. They worship themselves as being gods already, and their motto is something akin to "do what though wilt, shall be the whole of the law". They also teach a healthy dose of responsibility to go along with their doctrine, pointing out that it is only favorable to be responsible to others who are responsible for themselves.
"Devil" worship is usually practiced by fools and posers, A handful of pissed off Xtians who don't know anything except what they've been taught by the bible, and because they don't like god anymore, choose to do the opposite of what the bible says. Real Satanists despise these types of people because they really give us a bad name.
We teach that we are Natural beings, and as such, should do what comes naturally.
We teach that all the seven deadly sins are falsehoods, as they all lead to mental, emotional, or physical gratification. I could explain this in detail if I have to.
We also teach responsibility, that we are responsible for our own lives.
We teach that animals and children are sacred, as they are Natural in the most complete sense as they have not been sullied by the likes of preconceptions or interference from humans in an animals case.
We teach to love completely they whom deserve our love, and to hate they who would wish us ill, for then love and hate won't become watered down, by trying to love everyone, even people that do rotten things.
We teach to learn all we can about our natural world, to learn history and symbolism, so that we can better connect to Nature.
We teach an understanding of all the forces of Nature, and how to balance those forces within ourselves.
We show that self-preservation is the highest law, as if you cannot preserve yourself, then how you can preserve anything?
And we show how to ritualized our emotions into magical workings, to accomplish something that would otherwise be unchangeable, and to rid ourselves of emotions that if held in could destroy us.
We frown upon drug use, as that makes a person less effective as a magician and a human being in general.
I could write a book but not here.
Your friendly neighborhood Satanist

Courtesy of Phoenix M
http://blog.360.yahoo.com/blog-GY450_chc6m9woCEYAoOOMwhRha5?tag=religion
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used with permission