There are 52 cards in the pack, 13 cards (2-10, Jack, Queen., King & Ace) * 4 Suits (hearts, diamonds, clubs, spades).
All suits are equal in terms of ranking. Any hand in a higher ranking beats any hand in a lower ranking.

So, for example: any four of a kind beats any full house.
Between hands in the same ranking, the rank of the individual cards decides who is the winner.

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Royal Flush: This is the highest poker hand: Ten, Jack, Queen, King, and Ace of the same suit

Straight Flush: Five cards, all of the same suit that are in sequence.

Four of a kind: Four cards of the same rank - such as four kings.

Full House: Three cards of equal rank, and two different cards of the equal rank. (Three of a kind and a pair)- for example three sevens and two tens (colloquially known as "sevens full" or more specifically "sevens on tens").

Flush: Five cards of the same suit. If two or more players have flush then the one with the highest card wins.

Straight: Five cards of mixed suits, in sequence.

Three of a Kind: Any three cards of equal rank (also known as Triplets or Trips).

Two Pairs: Two cards of equal rank and a different two cards of equal rank.

Pair: Two cards of equal rank.

High Card: Five cards which do not form any of the above combinations. When comparing such two hands, the one with the better highest card wins.