It is a 4-card trick-and-draw game played by 2 or 4 players in fixed partnerships with a 32-card piquet deck consisting of the 32 cards of the ranks ace, king, queen, jack, ten and 7–9. Card suits do not play a role in this game, and there is no ranking order. Aces and tens have card-point values of 10 points each, while all other cards have no card-point value. Together with the 10 points awarded for winning the last trick, there are 90 points in a deal. The object is to win more than half of them, i.e. at least 50 points. A trick is won by the last player to play a card of the same rank as the card led.
Every player is dealt 4 cards. The remaining cards form a stock from which the players fill up their hands while it lasts. Eldest hand leads any card to the first trick. The remaining players are completely free in which card to play to the trick. The last player to play a card of the same rank as the card led wins the trick, is the first to replenish his or her cards from the stock, and leads to the next trick. The sevens function as jokers, i.e. they replace they assume the rank of the first card in the trick. However, if a seven is led to a trick, it just represents a seven.
Another explanation of the rules: http://sedmice.com/pravilaigre.php?lang=en