This is not a full explanation of Wicca. Look in the Writing Resources Links for pages that have a more complete explanation. Also, please note that not all Wiccans believe everything I've listed here. There are many different beliefs in Wicca and all of them are equally valid. (Thanks Calle for pointing this out!)
Wicca the Religion
Wicca is a religion that reveres nature in the forms of the Goddess and the God. This does not mean Wiccans worship nature. It simply means that the deities are seen in all living things and are treated accordingly. You certainly wouldn't disrespect your deity, therefore Wiccans do not disrespect nature.
Many Wiccans choose a pantheon of Goddesses and Gods (Celtic, Roman, Greek, Egyptian, etc.), though it is not required that one do so. Some Wiccans choose to simply worship the Goddess and the God rather than putting a specific name to Them.
One does not need to be a member of a coven to be Wiccan. Wiccans can be solitary practitioners as well, worshipping by themselves, designing their own rituals, spells, etc. Also, it is not necessary to find a "teacher" to learn Wicca. Many Wiccans learn by reading the numerous books on the subject, as well as informal lessons. Many feel that if you should have a teacher at a particular time, one will find you.
Wiccans have a very strong code of ethics. We will not perform love spells since that takes away a person's free will. However, lust spells, or spells to attract love (not directed at specific person) can be performed.
Wiccans do not worship Satan. It is impossible to worship an entity that one does not believe in. Wiccans do not believe in Satan and thus can not worship him.
Many Wiccans believe in reincarnation, or the rebirthing of old souls in new bodies. Between bodies, a soul rests in what is sometimes called the Summerlands (though it has many different names).
There are 8 Sabbats (or holidays) in a turn of the year for those who practice Wicca: Yule (circa December 21st), Imbolc (February 2), Ostara (circa March 21st), Beltane (April 30th), Summer Solstice (circa June 21st), Lammas (August 1st), Mabon (circa September 21st) and Samhain (October 31st). There are also 12-13 Esbats or Full Moons in a year, approximately every 28 1/4 days.
Wiccans do perform spells for all kinds of things. This is generally referred to as folk magick, rather than ritual or ceremonial magick which occurs on the Sabbats. Spells are not performed on anyone else, unless the Wicca has permission from that person to do so.
Wiccans utilize numerous physical tools to perform magick or for divination. Candles, herbs, gems, stones, runes, tarot cards are a few.
There are also numerous altar tools one can buy. They include: candles, an athame (pronounce ath-a-may) which is a ritual knife not used to cut anything in the physical plane, a broom or besom, a chalice or cup, a cauldron (yes, just like all the stereotypes, though generally used for burning herbs and not for potions), a bolline (ritual knife used to cut things on the physical plane), a wand, and an incense burner, among others.
"Wiccans do it Skyclad" is a popular bumper sticker. What does skyclad mean? Without clothes, naked. This generally refers to how some solitaries and covens performing rituals skyclad to be closer to the Goddess and the God (although many Wiccans also have ceremonial robes they wear for one reason or another).
Threefold Law: whatever one puts into the universe (be it good or bad) will come back to you three times over, so take care in your actions.
Yes, Wiccans do keep a Book of Shadows. This is where spells, rituals, research on gems, herbs, and divination are kept. It can also include just about anything one wants to add--including dreams, jokes, definitions of various magickal things, and contacts within the pagan community.
The Pentagram- no, it is not inherently evil as many believe. Each of the 5 points of the star represents one of the five elements, Air, Fire, Water, Earth, and Spirit. It is used for many reasons, including protection and increasing magickal energy, among others.
Main, all-encompasing tenet of Wicca: An it harm none, do what ye will.
Willow's Wicca is quite a bit different than the Wicca practiced by those outside of the Buffyverse...
Willow's spells often involve flashing lights or other such exciting imagery. This doesn't happen in real life (unless you manage to catch fire to your robes that is!)
Willow has also performed spells on others without their consent. The Will Be Done spell is a great example. Even though she didn't know she was doing it, she is still responsible for her actions (and baked cookies to make up for it, I think). Also, the spell in Season 4 on Oz...that could have caused her a lot of bad karma in the future years. Also, (Season 6 spoilers through 'Grave'!) the forget spell she did on Tara- she did not have Tara's permission, so according to the threefold law, she will get back what she gave. And lastly, she killed Warren using magic, which is in direct contradiction to the 'An It Harm None' tenet of Wicca.
Tara's cautions about powerful magick are valid. Real magick can occur and one should be fully cognizant of all the possible effects and outcomes before attempting a spell. This is something that Willow doesn't seem to understand quite yet. *grins*
*Season 6 Spoilers through 'Grave'* Willow was getting into the darker aspects of magick (though she stopped using magick altogether for a time and fought her addiction, with the events of 'Two To Go' she has since killed using magic and tried to end the world.) The spell she performed to get her revenge on Glory for brain sucking Tara is an example. Self defense or defense of others is permitted, but revenge is frowned upon. Witches try to help, not hurt, and generally believe that whomever is doing wrong will get their comeuppance due to karma later on down the road. Therefore, with Willow killing Warren using magic, she would have something threetime as horrible happen to her.
While Wiccans do have spellbooks, they are generally very private and personal books. Most Wiccans and witches prefer to write their own spells, believing it gives the spell more power if it comes from their own work. The big bookshelves full of spellbooks that is seen on Buffy is somewhat erroneous. While it is possible, it is doubtful that that are owned by one individual, and that all the books are readable. Especially when the books on Buffy seem to be extremely old. Most people did not know how to read and write at the times those books were apparently written. Therefore, it would highly unlikely for numerous books of that age to still be in good condition, if they are still in one piece at all.
Also, spells in the Buffyverse are very set in stone. There is a spell for uninviting vampires for instance. It requires certain things (herbs, etc.) and if it is performed correctly, it will work. In real life, a spell is a personal thing. Using another's spell could cause a different outcome or not work at all. Also, the ingredients are less important than the emotions and intent behind the spell.
Finally, the spells in the Buffyverse work almost immediately. Real life spells can take up to a month to come to fruition, so waiting and being patient is something all practicing witches/Wiccans learn quickly. Magic is not something to use if you're seeking immediate gratification- good results take time!
Have questions? Feel free to check out any of the sites in the Writers' Resources link page or Email me
*A majority of the information here can be found in Scott Cunningham's Wicca: A Guide For The Solitary Practitioner. If you would like a more complete list of books on the basics of Wicca, feel free to Email me!*