The full house is one of the strongest combinations consisting of three cards of the same rank and a pair along it.
For example, JJJ99 is a full house called jacks full of nines. Each full house combination is named by first mentioning trips and adding a pair like in the previous example.
With this hand, you will usually win many huge pots since it beats flush and everything below it and loses only to a better full house or quads, which is an extremely rare combination.
If two players have a full house, then you first compare who has the higher three of a kind to determine the winner. If both players have the same trips, then you compare the pair. For example, KKK22 is stronger than QQQJJ because trip kings are higher than trip queens. On the other hand, QQQJJ would win against QQQ99 because even though three of the kind part of the hand is the same, the first player has a higher pair along it since jacks beat nines. The pot will be split in half if two players have identical combinations.