Poker is a game of chance. However, when you introduce the concept of betting, poker gains quite a bit of skill and psychology. (This isn't to say that there isn't skill at poker when nothing is at risk, there just isn't nearly as much). This is meant as a very basic primer into the rules of poker, for more information, get a book on the game.

Poker is played from a standard pack of 52 cards. (Some variant games use multiple packs or add a few cards called jokers.) The cards are ranked (from high to low) Ace, King, Queen, Jack, 10, 9, 8, 7, 6, 5, 4, 3, 2, Ace. (Ace can be high or low, but is usually high). There are four suits (spades, hearts, diamonds and clubs); however, no suit is higher than another. All poker hands contain five cards, the highest hand wins.
Some games have Wild Cards, which can take on whatever suit and rank their possessor desires. Sometimes jokers will be used as wild cards, other times, the game will specify which cards are wild (dueces, one-eyed jacks, or whatever).