Tarot: Tarot Cards, Reviews, Readings & Community - Aeclectic Tarot has a lot of good basic information, too.
Tarot cards are dream symbols (in the Jungian sense) of many different human experiences and states of being, and when we lay them out in a reading, they allow us to see juxtapositions and connections we otherwise wouldn't. (Even the skeptics on this site ought to agree with that sentence--Tarot has the ability to get us thinking about our situation, about problems and solutions, in outside-the-box kinds of ways, even without anything magickal or psychic). I am one of those people who believes I am psychic, and I feel a deep connection to Tarot. Possibly because of my Romanian ancestry. Anyway, for someone like me, the Tarot is a very helpful body of non-linear knowledge (meaning you can start anywhere, with any card or combination of cards), but it is more than that. When I do a reading, and do it right, I feel I am guided both in what cards my hands pull from the deck and in how I understand the cards and the ways they relate to each other. It is a wonderful tool for making intuition stronger, just like a hammer or screwdriver is a wonderful tool for making your hand and arm stronger, to do specific kinds of work.
To a believer in magic, Tarot is an application of the first law of magic: As above, so below. Tarot cards work because on some basic level, the energy contained in the card is the same frequency or tone as the energy of something out there in the universe. When that thing in the universe, be it a person, an experience, an event, whatever, is important in answering the question asked by the Querant, when that energy is present in the Querant's life, then the corresponding Tarot card will be present in the reading.
Tarot is a little like Wikipedia. It wasn't created by just one person or one group of people with the right letters after their names. It is folk art and folk wisdom, created by many anonymous people over many years in many places in southern and eastern Europe, and now being added to by artistic people all over the world.
Want to know a secret? Once upon a time, long ago, there was a mysterious tribe of people living in Eastern Europe and Asia Minor who had all kinds of magical wisdom. These Magherae, or Machari, or Magi, served as scribes, magicians, and advisors to the kings of the ancient world. Those people travelled in all different directions. While they mostly kept their wisdom secret, sometimes they shared it, and so helped in the development of vedic, lamastic, kabbalistic, gnostic, shamanic, and druidic schools of knowledge. The Tarot is a tapestry with threads from many different sources, but I like to believe that in the center of that tapestry is a golden thread running all the way back to those people whose name is a human translation of the Atlantean word "Muur," which is the plural past reflective tense of the verb "to go." The Muur are "the ones who came from there." ;)