What are the Texas Hold'em poker hand rankings and how do they determine the winner in a game of poker?

In Texas Hold'em Poker, the hand rankings from highest to lowest are: Royal Flush, Straight Flush, Four of a Kind, Full House, Flush, Straight, Three of a Kind, Two Pair, One Pair, and High Card. The winner is determined by the highest-ranking hand at the end of the game, with ties broken by the next highest card in the hand.