the direction and amount of sand you want to pour into the bottle in each round. However, depending on the size and shape of the recipient, you'll want to let more or less sand fall at a time.
Likewise, to change the color of the sand, you just have to tap on the colors you see at the bottom of the screen. When you start the game, you'll see a ton of sand falling, even though the patterns on the bottles will have multiple colors. In this case, to change from one color to the next, you just have to tap on the color that matches the pattern on the container.
Sands is an incredibly simple game that requires you to fill bottles with colored sand until you get really impressive results.