At the start of the game, a shape will appear at the top of the screen, falling one square at a time. The speed at which it falls is determined directly by the level: if you select level 2, the blocks will fall twice per second; at level 9, they fall 9 times per second. (As the game goes on, things speed up, no matter what your initial selection.) When this shape “touches down” on the bottom of the field, another will appear at the top.
You can move shapes to the left or right, rotate them counterclockwise, or drop them to the bottom by pressing the appropriate keys. As you fit them together, completed horizontal rows vanish, and any blocks above fall down to fill in. When the blocks stack up to the top of the screen, the game is over.