Tarot cards are an ancient form of divination whose origins are shrouded with mystery and obscured by the thick fog of time. We know that Tarot was used in Renaissance Italy as a popular game, discovered by occult scholars in the 18th century, and connected to other forms of occultism by these same people. Many scholars have done extensive research into Tarot's origin, though their findings are often ambiguous and contradictory. Fortunately, the history of Tarot can be left to the historians; it does not matter to the reader. Where they came from, or when they were made, is immaterial. All that matters is that they are here, now, ready to answer your questions.
The practical answers to the question "What are Tarot cards" are as varied as they are numerous. They are an oracle that can answer questions about the past, the present and of course the future. They are a tool for guidance and for self-discovery. They are a way to get in touch with your own intuition and bring its powers to the surface. They are an intermediary between the conscious and the unconscious mind, through which the unconscious mind can communicate, and through which the conscious can understand. The Tarot cards are all of these things and more. One thing they are not is tools of Satan or the tokens of black magic.
At their most fundamental level, the Tarot is simply a set of symbols which are printed on a pack of 78 cards. Not good, not evil, just a deck of cards. These cards are shuffled and dealt just as ordinary playing cards are; in fact, a modern deck of playing cards is a smaller, slightly modified version of the Tarot deck. The Tarot has four suits with ten numbered cards and four court cards in each suit. (A modern playing card deck combines the Knight and Page into the Jack, leaving the King and Queen alone). In most Tarot decks there are also twenty-two numbered Major Arcana, alternatively known as Keys, Triumphs or Trumps. (Some authors will add or remove Keys but this is not a common sight.)
While the Major Arcana are the more powerful of the two groups, since they deal with major life changes and philosophies, the Minor Arcana are often the most common in readings because they refer to the mundane events most questioners ask about. (Mundane does not mean "boring" - it means "of the world", as in "of everyday existence".) Each of the four suits deals with a different general theme:
This is all well and good, but that is not what the majority of questioners are curious about. They want to know how Tarot cards can answer questions. Specifically, they want to know how a deck of randomly distributed picture cards can tell you anything about your future or about yourself, except through sheer coincidence. This is a question often posed by skeptics and beginners alike, and the key is that the cards are not randomized at all.
There is a power inside of the Tarot reader (and inside of the questioner, and inside everyone) that manipulates the cards without our knowledge. Some may call this the subconscious or unconscious mind; others refer to it as the Higher Self or the Soul. Some may attribute it to God or Goddess or another deity. I personally call it the Inner Voice. Whatever its name or origin, its function is the same. It projects itself onto the cards and, while they are being shuffled, it stacks the deck in the way that will best answer the question the reader are thinking about. Since the deck is face down, no one knows the difference.
This raises a very crucial point about the Tarot cards themselves. They are not full of magical power or touched by the curse of Satan, as skeptics and debunkers would lead you to believe - they are cards! All of the divinatory power of the Tarot lies with the Inner Voice and, by association, with the reader. This concept extends to all divinatory methods like Runes, I Ching, and the more obscure methods such as crystal balls and tea leaves. The Tarot is a tool that allows the Inner Voice to state messages in a visible form. While you cannot often hear the advice it gives you on its own, with the Tarot as its language, the message can be understood.
So it would seem that the deck is carefully sorted, not randomly shuffled. A deck of carefully sorted picture cards can tell you a surprising amount!