Each player has a hand of cards and in the centre of the table is a stock of face-down cards and a face-up discard pile. At the start of your turn you draw an (unknown) card from the stock or a (known) card from the discard pile (in some games you may be able to draw more than one card). You end your turn by discarding a card face up on top of the discard pile. In this way you try to improve your hand towards some objective.
All Rummy games use the draw and discard mechanism, the object being to collect matching sets of cards in your hand, or sometimes to meld sets by laying them out on the table.
Drawing and discarding is commonly used in commercial card games. It is one of the elements of many trading card games, in which the cards in player's hands and spread on the table before them are used to simulate combat. It is also often used ib board games in which the players hold a hand of cards which may enable them to perform various actions. The objectives of such games vary widely.