HistoryThe origin of the Tarot is uncertain if not positively controversial. Some occultists like to trace the deck's origin's back to ancient Egypt. However a more widely accepted theory is that the modern Tarot originated in Europe some time during the 14th or 15th Century.
It seems likely that the tarot was invented in Italy where is was used for playing games (specifically "tarocchi") - the divinatory usage came later. Initially this Italian Tarot was called Trifoni, a shortening of "carte da trifoni" which just means "cards with trumps".
What is a Tarot Deck?A Tarot deck is a pack of specially designed cards. Modern Tarot decks sold for for divination usually consist of 78 cards. 22 of these are individually named and numbered and are called the Major Arcana. The remaining 56 are the Minor Arcana, consisting of 14 cards of each of four suits.
The Major Arcana are of most symbolic importance and are always individually illustrated. The minor arcana might or might not be symbolically illustrated depending on the deck you choose to buy.
How Does Tarot Work?As with all forms of divination it's not clear exactly how Tarot reading works. Some people believe that the cards themselves have power and that the symbols tap into "something"; some even believe that the cards are inherently dangerous and/or evil.
Personally I believe that the cards and their potent symbols are simply a tool that helps to unlock the abilities of the user. Whether these abilities are psychic, unconscious ESP or just highly attuned perception and empathy really doesn't matter asd long as the reading works.