Polytheism is the spiritual concept of worshiping more than one deity (more definitions of polytheism: wiki, dictionary.com, or webster's). There are more flavors of polytheism than it's really ever possible to know. Primative cultures often had gods or ancestors to honor for different needs of the community: safe travel, good harvest, fertility, rain. Many popular ancient structures are used in some form today. There are some groups who adhere only to the traditions of Celtic, Greek, Roman, Norse, or Scottish deities. Other groups prefer to draw from many resources to aide in their practice; this is commonly called eclectic.

Paganism is the large heading under which witchcraft, wicca, traditionalists, Native American spirituality, and many other spiritual systems fall (see other definitions: dictionary.com, wiki, webster's). There are very few things that all pagans have in common. Modern pagans include witches, druids, shamans, healers, diviners, and many others. The main thing that pagans have in common is their lack of interest in converting followers -- I personally believe that one of the steps in showing you're ready to learn from someone else is being able to use your resouces to find an appropriate teacher.

Witchcraft is the practice of working with specific energies to acheive desired results. As a witch, I use many available resources -- plants and herbs, oils and extracts, smoke, fire, chanting, energy, different deities, making music, dancing -- to manifest what I am looking for. Many pagans use witchcraft within their practice of paganism, and many others do not.

Wicca is a nature based religious structure that honors eight holidays throughout the year. Wiccans have a set of ethics and codes to live by that are unique to what they believe in. Many Wiccans include witchcraft as a part of their practice, but the two words are not to be confused (wiccan =/= witch). Wiccans sometimes use the Rede as their moral compass. This modern movement was initiated in the 20th century by Gerald Gardner in England, though Wicca today is not always as he envisioned it becoming.

Don't you worship Satan?

The pentacle is a sacred symbol to many pagans, witches, and Wiccans just as a cross is sacred to a Christian. The thought that it is sometimes used in association with worshiping Satan or harming children is just as ghastly to us as it is to everyone else. The pentacle has been mislabeled by our society as something evil, when really it is very pure.

In paganism, the pentacle most commonly represents the five elements: earth, air, fire, water, and spirit. The pentacle is symbolic of stability, unity, and balance. I don't worship Satan, and you won't find many Pagans who would say they do either.

What about the wild orgies and nude worshipping?
In most pagan communities, sexuality is something celebrated rather than stiffled. There are groups who prefer to worship without clothes, and who incorporate sacred sexual acts into their rituals. I've never heard of a public ritual being performed skyclad -- that is, without clothing. This practice was made popular by Gerald Gardner when he was teaching Wicca in England in the 20th century. I've personally never had any desire to practice skyclad. Some say that it's freeing and humbling being naked, but mostly I think it's cold and uncomfortable.

Can you help me fall in love with my crush? Please?
Responsible witchcraft comes with respect of the boundaries and guidelines of what you're doing. It's certainly not impossible to make someone fall for you, but the repercussions of that crush may be devastating. Magic must be worked carefully because the results will come back to affect you -- this is the three-fold rule (some call it ten-fold, some call it two-fold). So, no, I can't help you make your crush fall in love with you (and no other self-respecting witch should either!).

Aren't you in a cult?
Witchcraft, Wicca, and paganism are not cults. They're officially recognized spiritual practices that are mostly self-driven (or locally driven). There may be groups claiming to be magical who are involved with a cult, but it is not true paganism. The groups I practice with do so well within ethical and moral boundaries.

druid: an earth based religion I'm just getting into (ie, I know nothing of interest to share yet).
eclectic: made of parts of many different spiritual paths
traditional: of one of the traditions of Wicca or witchcraft (ie, Gardnerarian, Alexandrian, British Traditional Witchcraft, Feri Witchcraft, Reclaiming, Regional tradition).
coven: a group of witches who gather regularly to celebrate and practice
sabbat: a major holiday; in Wicca, there are eight sabbats.
esabat: a minor holiday; in Wicca, the esabats are celebrated on the night of a new or full moon.
altar: a surface dedicated to ritual things with the working purpose of worship.
pentacle: a star shape that is sacred to the element of earth as well as being representative of the five elements working together.
wand: usually wooden, a wand helps the user project energy out from their body by chanelling it through the wand.
chalice: a ritual goblet or cup
cauldron: an iron or steel pot for ritual fire
ritual: involved sacred theater with the intent of honoring the time of year or the events happening in one's life.

Here are a few links for those who are more interested. It's nothing that you couldn't get from a google search if you were so inclined. Please do me a favor and understand that there's a lot of truth in the pagan quip, "Ask three witches a question and you'll get seven opinions."
Alt.Pagan FAQ
How I Became Polytheistic
A Great FAQ
Witchvox.com Basics Page (Witchvox.com is well known among the Pagan community)