For those who are still not familiar with the game, this is a quick break. Texas Hold'em is a casino card game that runs from two people to nine or so. In each round, each player gets two cards from a common deck - they must keep them. There is no card change or new card in Texas Hold'em.
After the first two cards were traded, there was a round of betting. Then, after that, the three cards in the deck are "flip" onto the table - these are the common cards that everyone uses. There is another round of betting, then the fourth card enters the table.