Click on Play to begin and then on the first Buoy as that is the first level.
Your objective is to bring the divers safely out of the water. To do so, you must eliminate the colored blocks in their path. You must click (with mouse or finger) on 3 or more blocks of the same color to remove them. On the way you will also have bonus blocks such as penguin (penguins come and remove some of the blocks), bomb (explodes and destroys blocks around it) and others.