There's falling blocks, with different colors and shapes, and you must put three of the same color together in order to destroy them. Be careful, because they are flashing pieces that will rise the floor one line to the top if you destroy them.
Arrow keys right/left to move horizontally, up to rotate, down to drop. At top and right there's an information bar that gets red-colored as you advance in the game. At a certain moment this bar will notify you to press the space bar: by this action you will remove all the flashing pieces at once.