Tarot cards first emerged in Europe in the mid 15th Century. For a long time they were simply used for playing games; it was not until the late 18th Century that they became associated with divination and the occult. Like a conventional pack of cards, the Tarot has for suits, collectively known as the Minor Arcana: Cups, Coins, Wands and Swords. These include the four court cards of King, Queen, Knight and Page, as well as ten numbered cards. There are also 22 cards known as the Major Arcana, which are not numbered but represent a journey taken by the first card, The Fool. The subsequent cards include Justice, The Wheel of Fortune, The Devil and Judgement. In their modern usage, each card holds particular symbolic meaning; drawing a spread of cards, in a particular sequence or arrangement, is said to reveal hidden truths to the person reading them. Possibly the most popular deck of Tarot cards is the Rider-Waite, but there are many different variations, and browsing through a selection is an interesting exercise.
For more in depth information, this Tarot website is a great resource. They use a considerable variety of decks and explain in great detail the meaning behind each card. You can also have a free online reading, if you're curious.