You can erase same pieces which are connected vertical or horizontal, as you click them. If there are pieces over the erased pieces, they will drop down. If all pieces on the vertical line are erased, all pieces on the right side will slide left.
The score is ([the number of erased pieces] - 2) ^ 2. Therefore, connect same pieces as more as you can, and erase them at a time, so that you can aim the higher score. The game is over when there are no pieces to be erased.
The score will be decreased as the number of remained pieces. If you erase all pieces, the bonus points (1000 points) will be added to the score.