Like rubber bridge, duplicate bridge is also played by partnerships. You and partner (your team) will be sitting North-South or East-West.
Whereas the objective of rubber bridge is to maximise your score for a rubber, i.e. a series of hands, the objective of duplicate is to maximise your score for the hand that you are playing.
In duplicate, the hands are pre-dealt. At the same time, vulnerability (neither, NS, EW or both) is randomly assigned, unlike in rubber bridge, where the vulnerability is determined by prior play. Once a hand is complete, the cards are not shuffled but placed face down ready for another NS and EW to re-use the same deal.
Importantly, rather than considering your competition as being your opponents at the table, you are competing against other partnerships who are playing the same deal. Thus you can be rewarded even if you have an awful hand, if you play it more skillfully than the others.
The scoring is standard contract bridge scoring, with a few very minor differences from rubber bridge. But, the fact that you are playing hands in isolation, not part of a sequence of games, will often completely change your objectives and strategy in play, compared with the same hand in a rubber. For example, there is little value in obtaining overtricks in a rubber, when declarer can play more safely for game. But, for duplicate, your merit is based on differential score, hence extra points for overtricks could be all important.
This is a competition played by 8 people. This requires packs of cards pre-sorted into the same sequence.
The same deal occurs simultaneously on two tables (which cannot see or hear each other, for obvious reasons). In these competitions, you and partner get to play three hands - against each of the other partnerships.
Larger duplicate competitions
These involve having a number of pre-dealt hands, each given a board number (the cards can be stored face downwards on a board). The players play on a number of tables, usually isolated from each other in a specially suited venue. For example, if you play board 5 EW, you are playing against all of the other partnerships that have played or will play board 5 East-West.
Your partnership's cumulative score is based on how you have fared compared with other partnerships playing the same hands at each board. These scores are summed across all the boards in a session.