Wicca has nothing to do with Celtic pagan religion. it was "invented" by British civil servant Gerald Gardner in the 1940's and 1950's (he went public with it in 1951 after the repeal of anti-witchcraft laws in Britain). he pieced it together out of many things, some of it being golden dawn and ThelmaICCitual magic, some of it being Arthurian legend, some of it being British folk magic, and a good deal of it being pop-anthropology of his day (much of the last category being later disproven). there's some other stuff in there as well.
the two best books to start your research with are "drawing down the moon" by margot adler and "triumph of the moon" by ronald hutton. after that, start reading some of the books listed in their bibliographies. feel free to pm me if you'd like further assistance.
A book that may help get you started is the Encyclopedia of Magic and Witchcraft. It briefly covers many different pagan believes from around the world. I don't claim to be an expert but I have some information on the subject if you have a way I can get it to you, since it's too much to post here let me know.
Wicca is a modern amalgamation of traditions from many different non-christian or "pagan" cultures.
As many different "pagan" religions as there are, there's no such thing as paganism, unless you decide you believe in everything that isn't christian.
There are a lot of modern "alternative" religions that are based basically on not being christian. This means they are still defined in terms of Christianity, so they're not entirely free of it. The weakest of them all are those who say they're "satanists," considering Satan is a christian god. Just like Hades is a Greek god.
My coven teaches an eight week course on the basics. That's a great deal more than can be answered in a post on a message board.
As for the Celts, no, not really. Although many (most) Craft traditions do work with Celtic deities, the religion known as Wicca really got off the ground with a British gentleman by the name of Gerald Gardner who added elements of ceremonial magic to the incomplete liturgy of the Craft he was initiated into. There are Wiccans who come from a "sister" line of that which Gerald started and are recognized as Wicca today, but as with any family, there are politics involved.
Wicca originated in England. It was created by a civil servant named Gerald B. Gardner, somewhere between 1930-50. He **based** his religion on Prue-Christian practices however also piecing his religion together from the practices of the "Golden Dawn" as well as some Freemasonry (see link below, follow link within to "The real history of Wicca).
It's basics are that they are a polytheistic religion in which they worship a Goddess and God (the pantheon differs from tradition to tradition or person to person), stress on duality and balance, observes seasonal events, believe the deities are not off on some distant cloud, but live amongst them as well as within, and stress on responsibility for ones actions. They live by the guideline "An it harm none, do as thou will" (Not "Harm None"), in which means to inflict as little harm as possible, as living a life completely harm-free is impossible. It makes the follower think about his or her actions before they take them to see if it's really necessary or could other steps be taken.
Here is a site that could help you better understand Wicca:
http://wicca.timerift.net/wicca101/Basics.shtml#1
As far as can be pr oven outside the oath bound secrets of the tradition, Wicca was started in the 1950's by Gerald Gardner in England. He based the tradition off of possible witchcraft teachings of the New Forest area (although there is nothing beyond his word to prove it), Crowley's teachings, and some bits and pieces from other parts of the world.
What are the basics of Wicca and did it originate with the Celts.?
