The origin of Tarot is unknown, although everybody seems to agree that the most certain ancestor of the Tarot is an egyptian book, called 'The Thoth Book', in which some students have found the representations of the 22 cards of the Major Arcane.
There is a book, called 'Le Monde Primitif' from 1781, where Antonie Court de Gebelin explains that the Major Arcane cards may, in fact, be a reproduction of the 'Toth Book'.
But it is not until the 15th century, in Italy, when a card game called 'The Game of Triumphs' was invented. It was originally a game, not for divination purposes, but it was made of symbolic picture cards, the same as the Major Arcane.
The popularity of this game made it spread to Germany and France, in succesive centuries, where it changed and a few cards were added to the deck. There were also some changes on the pictures, and some creative decks were created by locale artists.
When it became used for divination purposes is not known, but it seems that the occultist sects of France and Italy lasted not long to use the Tarot cards for this purpose.
Today is very common to make readings using Tarot cards, and nobody knows why, but once you try it, you get caught by its mistery, and this is the reason for this site to exist.