The squares of one color placed side by side form a block (one square is not a block). When you move the mouse over the board, blocks are highlighted. If you click on a block, it vanishes, and the squares above it shift down (and left if an empty column is created). The more squares in the block, the more points you get - the number is shown on the right of the board. The game is very strategic in nature - if you think a few moves ahead, you can assemble larger blocks that gain you much more points.