The aim is to use the descending blocks to build up from the bottom of the screen. Every row you complete is removed from the board and all the blocks move down accordingly.
If the blocks reach the top of the screen, the game is over. You can rotate the falling blocks as they come down, using the Up arrow.
Move the blocks left and right with the Left/Right arrow keys, and drop the blocks to the bottom with the Down arrow. To toggle the grid on and off, use the G key. Have 3D fun!