http://www.religioustolerance.org/wic_sata.htm
Overview:
Although the words "Wicca" and "Wiccan" are relatively well defined at this time, such terms as Satanism, Paganism and Witchcraft have many meanings. Confusion over the definitions of religious terms is quite common. Even the term "Christian" is defined differently by various groups. The sentence: "Ann was raised a Roman Catholic but became a Christian later in life" might be quite understandable to an Evangelical Christian, but wholly confusing and probably quite insulting and distressing to a Catholic.
Some people sincerely believe that over 75% of the human race (including Wiccans) are followers of Satanism. Others, including Satanists, Wiccans, religious historians, many theologians, those mainline and liberal Christians and individuals who are knowledgeable about minority religions, etc., consider Wicca and Satanism to be two unrelated groups of religious traditions. They share few points of similarity. In fact, many of their beliefs and practices are diametrically opposed to each other.
There is no right or wrong definition in these cases. Groups simply assign very different meanings to the same English words. The sentence: "Wicca is a type of Satanism" is neither right or wrong. Debate is useless. It is a true statement to one group and false to another.
Satanism, as viewed by Satanists, etc.:
Satanism consists of many religious traditions, comprising two main faith groups and many smaller religious groups:
The Church of Satan is the largest organization of religious Satanists. They regard Satan as a pre-Christian concept, representing pleasure, virility, and strength; he is not viewed as a living entity. Their prime symbol is the Sigil of Baphomet. This is a goat's head, drawn within an inverted pentagram (5-pointed star with one point downward and two up). It is surrounded by a circle. Satanists conduct rituals by themselves, and/or meet together in grottos.
The Temple of Set worships Satan in the form of a pre-Christian deity -- the Egyptian god Set. Their prime symbol is a simple inverted pentagram in a circle. They meet in temples.
The behavioral code followed by almost all Satanists was written by Aleister Crowley: "Do what thou wilt shall be the whole of the Law." It permits Satanists great freedom of action. Some engage in black magic rituals with the goal of harming those who have hurt them. Turning the other cheek is not their style.
Wicca, as viewed by Neopagans, etc.:
Wicca is unrelated to Satanism. It is a group of religious traditions: some are highly structured, while most are eclectic. Many, perhaps most, Wiccans are solitary practitioners. They are, in many ways, directly opposite to Satanists:
Wiccans worship a Goddess and her consort, a God.
They do not recognize Satan or any other all-evil supernatural entity.
Their prime symbol is the exact opposite to the symbol used by Satanists. It is the upright pentagram -- a 5-pointed star with two points downward and one up. Sometimes it is enclosed by a circle to form a pentacle.
Their groups are called covens, not grottos or temples.
Their rule of behavior is called the Wiccan Rede: "An it harm none, do what thou wilt." i.e. do whatever you wish, as long as it harms no one, including yourself. Unlike Satanists, Wiccans are not allowed do dominate, manipulate, control, or harm others.
They believe that they worship neither the Christian God nor the Christian devil. They worship a Goddess and a God. Neither is at all similar to Satan. Wicca, and other forms of Neopaganism, are as different from Satanism as Hinduism is from Christianity.