In every game, all the players receive some given number of cards. To play one hand is to play a series of tricks, where each player chooses one of the cards in their hand and plays it to the middle, and one of the players ends up winning the trick. Usually, the hand is finished when all the cards have been played in tricks, and deal rotates to the left and a new hand starts.
A trick is a single rotation, where everybody playing plays one of the cards in their hand to the middle. One person leads, or plays first, and then play proceeds to that player's left, until everyone in the game has played one card. A single person then wins the trick, and takes the cards that were played to signify they've won.
The rules that determine what a person may lead, what others may play after, and who wins are the meat of most games.
In most cases, the first person to play to a trick may select any card in their hand. The suit of that card—clubs, spades, etc.—determines the suit that must be followed. Most commonly, if subsequent players have another card of that suit, they have to play it. They can only play a different suit if they have no cards of the suit that was led.
In the simplest format, the winner of the trick is whoever played the highest card of the led suit. Whoever can't follow suit, even if they can play a higher card, can't win the trick.
An extremely common feature of trick-taking games is trumps. The method of determining trumps varies from game to game, but many different games feature a suit—usually for the duration of a single hand—that can "beat" other suits. In these games, players who can't follow suit have the opportunity to trump, or play a card of this suit, if they've got one.
In games with trumps, the winner of the trick is whoever played the highest card of the led suit—unless someone played trumps, in which case the highest trump wins. Even if the trump card played is lower in rank than the highest card of the led suit.
Here are two examples of a simple trick-taking game that illustrate the mechanism above. They'll represent the four cards played, in order, by four players. We will say that in these examples, clubs are trump.
10
Spades were led, so everyone who could play spades had to. The second card was the deuce of spades, which couldn't beat the ten. The third was the jack of hearts, which was off-suit (ie, not what was led and not trumps) and so couldn't hope to take the trick, even though numerically it was higher than a ten. The last player played the jack of spades, which was higher than a ten and in the suit that was led, so that player took the trick.
A
In this case, spades were also led, so anybody who had spades had to play them. The second player played a lower spade, the 8. The third player had no spades; in this case, however, they did have trumps (clubs in this example), and were able to play the king of trumps. Trumps are always higher than the led suit, so they were winning the trick at that point. The fourth player still had to play spades, however, as the led suit was still in effect, so player 3 took that trick.
Most games keep track of player scores by counting who took the most tricks in any given hand, or sometimes by assigning point values to individual card ranks and counting who took the most points.