Follow the color.

Press a dot and drag. The trail follows every dot of the same color you touch, including the ones on a diagonal, so it can turn corners and double back around the board.

A dot can only be in the trail once. Lift your finger on a trail of three or more and those dots clear, the dots above fall in, and new ones drop from the top.

Each level asks for a number of dots in one or two colors, shown in the chips above the board. The length of a trail is what counts, so a long trail in the color you need is worth more than two short ones.

A trail shorter than three dots does nothing and costs nothing, so look around as much as you like. Run out of moves and you get a brand new board for that level, and the levels you have already cleared stay cleared.