The following is a list of 5-card poker hands, from the absolute best to worst. This list assumes no jokers or wild cards are being used.
A royal straigh flush is when you have 10-J-Q-K-A, all of the same suit.
Five cards, of the same suit, in order, such as 4-5-6-7-8 all of hearts.
Four of the same card, such as 8-8-8-8-5.
A set of three of a kind plus a pair, such as 10-10-10-3-3 or K-K-K-2-2.
Five cards all of the same suit, but not in order, such as 2-4-7-J-K of spades.
Five cards in a row, such as 3-4-5-6-7, but not all of the same suit.
Three cards of the same number or rank, such as 6-6-6. If you had Q-Q-Q-2-3, you'd have three of a kind.
Two pairs of cards of the same number or rank, such as 5-5-4-4. If you have a pair of sevens and a pair of nines, you've got two pair.
Two cards that match, like K-K.
If no one has any of the above hands, the player with the highest card in their hand wins. Just having an ace in the hole is sometimes enough.