That's a hard question Mini, you can write books about it...
Here's how I see things:
There is no such thing as Satanism in general like you have
The One truth in christianity. The main difference is the way Satanism is practiced and percieved and what role the Satan/devil etc gets.
Classical Satanism: this is the satanism you've heard about in history class. The old way in which
Satan is the pole of
GOD and puts him as an equal. This religion is no better than Christianity as it is as submissive and fairytale-esque.
Laveyan/ Modern Satanism: aha the famous one. 'Founded' by La Vey and
Head of the Church of
Satan, and a later spin-off is
The Temple of Seth. I won't go into detail on his views but just know that atan isn't really seen as a
GOD here... more like an idea, a way of life and thinking. In some way I compare the perception of transcendence to Buddhism. Just wiki buddhism and make links in terms of transcendention.
'metal' satanism: okay... what's this? This is an amalgame of
Ideas taken from both Laveyan
Ideas and ideas/lyrics given by bands etc. It's like you would shop into satanism and take the
Ideas you like (individualism etc)
others: all sorts of strange sub-sekts, each with their own sick or less sick ideas. Some actually believe in a living
Satan
Link paganism: There are some links yes but they are rather vague. First of all: the satanic
Pentagram is the upside
Down version of the Pagan/Wiccan
Pentacle which was a symbol of connection between the elements. Satanism is highly individualistic which might reflect in some
Pagan sects but not all, certainly not in neo-Slavonic ones
hope it helps
I always thought that the definition of the word Pagan that I was taught was pretty vague.. 
