What is Satanism really about?

Do they really worship Satan? Or is it just a representation of something else?

Depends on which Satanism you're talking about. There is spiritual Satanism and LaVeyan Satanism. LaVeyan Satanism is atheistic but spiritual Satanism actually views Satan as an actual being or force.

JoyofSatan . com Find out yourself. The other kind of Satanism is atheism.

Satanism is a religion based on self-worship, modeled after the ultimate selfish, anti-authority and pro-self mythological figure: Satan.

Satanists do not worship Satan, they worship themselves and their natural desires.

There are a few types of Satanism. So in answer to both your sub-questions, yes.

Actually we worship the ancient gods who were demonized by the christian church read WNW.joyofsatan.org for more details.

Knowledge, enlightenment, truth, liberation... It is the original religion. The religion of Christianity is a lie.
Satan does exist, and is not just a "concept", as some say.