After completing 'Inside Jabu-Jabu's belly', go to the hyrule field. You will see the evil gannondorf chase princess Zelda. She will throw the ocarina of time in the water. Dive and get it and she will teach you the Song of time.

Note: Play the Song of time somewhere in the temple of time and you will realease all three stones. The door will open and you will get the Master Sword!! You will also grow up to be an adult.