One way is to not tell anyone about it and keep it to yourself. You could also store it in a private online account that only you have access to.
One way to do it is to write it in a code or a language that only you understand. But that can be quite complicated. Or you could store it on a password-protected digital device and never share the password.
Well, you could write it in a language that only you know or use some sort of code. Just make sure you remember how to decode it later!
It depends. If you keep your story completely offline and don't share it on any online platforms, then yes. But once it's out there, it's hard to control who sees it.
Well, it might be difficult to hide it completely. There are always chances of it being discovered or accidentally revealed, especially if it's something significant.
You could keep it in a private diary and lock it up.
You could keep it in a private folder with a password. That way, only you know how to access it.
Well, one way to do it is to make the main character have a solitary adventure in a remote area. Or maybe have a catastrophe that scares everyone away. But this might require some careful world-building and plot development to make it believable.
You might consider not writing it down at all and just keeping it in your mind. Or, if it's something physical like a paper, store it in a locked box in a hidden place.
You could keep it in a private diary or journal and lock it away.
You could keep it in a private journal or password-protect it on your device. That way, only you have access.