Texas hold'em poker is a card game. It is played with a typical 52 card deck. You can find it in countries all around the world in casinos to cardrooms, online and in home games. Hold'em can be played with as little as two players (going "heads up"), up to a max of eleven players. Regular poker hand ranks apply to this game. The typical hold'em game goes as follows and is broken down into five categories. I have intentionally simplified betting and the blinds so not to over complicate the article. Betting structure can be read more about here:

Preflop: Starting with the dealer button, each person is dealt one card. Then a second card. Both cards are face down. After everyone receives their pocket/hole cards (the two cards face down just dealt), then betting occurs. Note: the dealer button is a actually a button that says "dealer" on it or "d" that is passed around the table after each hand. It signifies where the dealing is done from.

Flop: The dealer turns over three cards in the middle of the table (called "the flop"). These are community cards that each player can use to create the best hand possible out of. Once again betting occurs.

Turn: The dealer turns over another card making four community cards. This fourth card is called "the turn" or sometimes "fourth street". Betting occurs again.

River: The dealer turns over the fifth and last community card. This is called "the river" or "fifth street". Betting occurs for the last time.

Showdown: The remaining players in the hand show their cards in order from the person who bet first. Each player uses his two cards, and the five community cards to create the best hand (5 cards total). A player can use any combination so even if one card from his pocket cards and four of the community cards creates the best hand, it is fine. When all five of the cards in the community make the best hand then everyone splits the pot. This is called "the board plays". Also note that in any time during the game a player can fold and get out of the hand. All bets will be lost at that point.