Royal flush
This is the strongest hand in Poker. It consists of a 10, Jack, Queen, King and an Ace of the same suite
Straight flush
This is the second strongest hand you can have. It consists of cards in a continuous order of the same suite.
4-of-a-kind
This is when you have four cards of the same value in different suites.
Full house
A full house consists of 3-of-a-kind and a pair. I.e. 3 nines (3-of-a-kind) and 2 twos (a pair)
Flush
A flush consists of 5 different cards of the same suite.
Straight
A straight consists of five cards in consecutive order.
3-of-a-kind
This hand consists of three cards of the same value of different suites.
Two pair
This hand consists of two pairs of cards of the same value.
One pair
This hand consists of one pair of cards of the same value.
The above hands are ranked from strongest (Royal Flush) to weakest (one pair).