Tetris in its most basic form is very simple. Tetronimoes, that is, shapes made of four square blocks, fall down the screen and between two walls. Your job is to move the tetronimoes as they fall, rotating them when necessary, to fit together as complete rows of blocks. Each time a row has been filled, it disappears, leaving room for more tetronimoes. If too many pieces fall without complete rows, and the pile of blocks reaches the top of the screen, the game is over.
Some variations of Tetris offer extra goals or challenges. Many early versions, including the first PC edition, have an option to start the game with part of the screen already filled with incomplete rows of blocks. Some versions have special rewards for completing a certain number of rows. Some editions feature two-player capability, for cooperative or competitive play. Even with these extra features, however, creating complete rows remains an essential part of the game.