There are two forms of Croquet that are commonly played in this and other countries: Association Croquet and Golf Croquet. They have different rules and tactics, but use the same courts and equipment (hoops, balls and mallets) and have the same basic objective of getting a ball to go through a hoop. In both games the Red and Yellow balls play against the Blue and Black, either as doubles, in which each of the four players has one ball, or singles, in which each player has both balls of a side.
Golf Croquet has the simpler rules and is the more interactive game. Each turn consists of a single stroke and the balls are played in strict sequence: Blue, Red, Black, Yellow, then back to Blue again. Each hoop is a contest in its own right: the side whose ball first scores it gets a point and then all balls immediately go on to try and run the next hoop in order (as with matchplay golf, after which the game is named). As soon as one side has got the agreed number of points (normally 7), the game is over.
Association Croquet is like snooker in structure, in that a turn can consist of more than one successful stroke, in which several points can be scored. The winner is the first side to get both its balls round the course of hoops and hit the peg in the centre of the lawn. Extra strokes are earned by causing the ball you are hitting with your mallet (the "Striker's Ball") either to run its hoop or to hit another ball. The latter is called "making a Roquet" and entitles the striker to two extra strokes: a "Croquet" stroke, before which the striker's ball is picked up and placed in contact with the ball it hit, and a continuation stroke played from where the striker's ball ends up.