Sometimes you don't want your Story to be found in the different search engines. Think of it as unlisting your YouTube video. You can unlist your Tappable Stories.
It can be because:
It is an internal document
it is a promotional campaign
...
When you're ready to publish your story, press the preview button fill in your meta informations.
And uncheck the "allow discovery by search engines" check box!
And that's it you're story won't be able to be indexed by search engines.
Happy Story creation.