Declarer makes a claim by placing his cards face up on the table and announcing that he will win one or more of the remaining tricks. A defender makes a claim by showing any or all of his cards to declarer and announcing he will win one or more of the remaining tricks. When a player makes a claim, he should state his intended line of play. If he fails to do so and an opponent contests the claim, restrictions apply to his play. In duplicate, if anyone disputes a claim, the players should call the Director to adjudicate.
Claiming, if done well, speeds up the game and so is generally a good idea.