You need a Google Play Games account to saved/load your progress with Google Play savegames. Once you are signed-in in Seashine with your Google Play Games account, the game will automatically save your progress to the cloud when you exit the app. It will load your progress when the game starts if there is any progress on your cloud saved game compared to your local saved game.
Your unlocked jellyfish, unlocked abilities, third ability slot unlock, and your discoveries will be automatically saved to your Google Play Games account.
Deleting and reinstalling the game, or simply installing the game on an other device with the same Google Play Games account you used to save the game will automatically restore your progress when the game starts.
Please note that you need an active internet connection to load your saved game from your Google Play Games account.