Church of Satan is an open worship of Lucifer by the name of Satan. It is the same Occult empire that is affiliated with modern Witchcraft. They function as a means of organization, and indoctrination of people that lead local covens and meetings.
The church often gains interest of spiritually uncertain people by their claims of being in harmony with nature. It is this exact sentiment of rebellion and worshiping the earth or gaia that is opposed to the wishes of the Will of God, expressed to man through the Holy Bible.