From the Game's Introduction:
The sea is teaming with stories and adventures. Under the waves is a virtual symphony of life ripe for players to explore with their imaginations. All sea creatures sing - though Lubbers (what ocean-life calls any creatures on land - including humans) can rarely hear it. Each aquatic creature contributes to the overall symphony of the ocean. And what a wonderful symphony it is! If you stand quietly on the beach early in the morning and listen carefully, you can hear it.
Role-Playing is, at the core, "let's pretend". It's not really any different than when you played Cops & Robbers or Cowboys & Indians or whatever other pretend situations you could envision as a kid. Octopus' Garden is a codified set of rules to help govern this world of make believe and turn it into a more structured game. Now, there isn't anything wrong with no-rules make-believe playing - but some may find it rewarding to impose some minimal structure onto the playing and turn it into a game. Octopus' Garden is designed with a minimum of rules which mostly stay out of the way and allow your story to take center stage. Open up your imagination and have fun!