While Animal Crossing: New Horizons automatically saves your game at regular intervals and upon certain actions (like entering or exiting buildings), there isn't a traditional "save" or "load" option accessible directly through the in-game menus in the same way you might find in other titles. Instead, the game utilizes a robust autosave system combined with a specific method for backing up your island data to the cloud.
Understanding how this system works is crucial for safeguarding your progress and ensuring your island remains intact. You won't be able to manually "load" an old save file if you make a mistake, but you can recover your island data if your Nintendo Switch is lost, stolen, or damaged, thanks to the Island Backup feature. This feature becomes available a little later in your island development.
For now, simply be aware that your game is constantly saving your progress. When you're ready to stop playing, simply close the game from the Switch Home Menu. There's no need to find a save point or manually trigger a save.