Stones (with a strange metal look) are falling from above. They have different sizes. Some are just squared, some are rectangles. You can move the stones to left and right after they have landed. On the easiest levels the stones come in waves, in the more difficult levels the stones almost fall all at ones. Try to move the stones so there will be as few gaps as possible. Sound easy, yes, sometimes it is, but the magic with StonePacker is that is so fun to play, to move, to pack the stones. There are two versions on the market, one called StonePacker with two levels and medium board sizes. The other version is called StonePacker Pro and has 3 different stone/board sizes and 100 levels.
Have fun with StonePacker.