That's all literally explained in their FAQ though.
https://www.churchofsatan.com/faq-about-the-organization/
> LaVey used “Satan” as our primary symbol, employing the hebrew term predating Christianity meaning “the opposition, the accuser”—it was later personified, perhaps accidentally, as part of a mistranslation. We use this term as it was originally defined, for we stand in opposition to theist religions and their inherent hypocrisy. We are a formidable threat to any who would halt progress in the name of spirituality. We are explorers on the untrodden paths of science, human motivation and all mysteries awaiting understanding.