the quick answer is:
There Is No Such Thing!
Have a look at the official scrum guide.
Have a look at the original (IMHO) Scrum book by Schwaber and Beedle.
Have a look at the OOPSLA’95 article that introduced a broader audience to Scrum.
None of them mention stories!
There is a lot more to know about stories of course – Mike Cohn wrote a Book on writing user stories and defined one of the best known formats for writing stories (although there are many other opinions and additions)and Jeff Patton popularized the idea of story-mapping in a very approachable way.
But those are not things that Scrum defines, requires or in any other way endorses. Those are all additions by the community that might fit your case. Or not. Give it a try. Evaluate cautiously. Pick what works for you.
till next time