Piquet is a game of exchanging cards, declaring points, sequences and sets, and then playing off the cards as tricks. What you exchange will affect what you can declare, and what you declare will provide insight to the cards you hold and therefore affect how your opponent plays to the tricks. Points are accumulated for both declarations and tricks - so a carefully balanced strategy is the key to winning.
A Partie (or game) is comprised of six rounds, three dealt by each player alternately. The non-dealer exchanges one or more cards with those that remain undealt, then the dealer exchanges up to as many as are left. If any cards remain untaken after the exchanges, the dealer may elect that they be displayed face-up for both players to see.
The declaration phase starts with the non-dealer declaring their point - i.e, the longest suit. The player with the better point wins the point declaration. Then sequences (runs of consecutive cards of the same suit) are declared, and finally sets (cards of the same face value). If a player wins a sequence or set declaration, they may declare any other sequences or sets that they hold.