You have to collect the 4 objects that are scattered on the bottom of the sea and, when you have them all, bring them back to the boat. This is the objective. To do this, you must be careful not to lose all your oxygen. The way to lose it is by touching plants or bugs that swarm around the sea? well, just being underwater makes you lose it little by little. To recover it: go up to the surface or collect bubbles that you'll find hidden around? each bubble gives you one life, that is, 100 more units of oxygen. You start with only 100 units of oxygen, and as you lose oxygen, you get weaker and weaker... so get your oxygen!