Falling blocks stack up from the bottom. Fill a complete row with no gaps to clear it. If the stack reaches the top, the game ends.
Controls: arrow keys (left, right, up to rotate, down to speed up, space to drop) or the on-screen buttons. On a phone you can also tap the board to rotate and swipe down on it to drop. Clearing several rows at once scores much more. Every 10 lines you go up a level and the blocks fall faster.