Action Details
Requirements and how-to articles for YouTube's action:

Create a post to go in your "story." (Currently only available for accounts with at least 10,000 subscribers)

You need this to get it done:

Create Story Post
Add a short video to your Story.
Requirements missing or found errors? Report

How-To Articles
A list of useful links for you:

YouTube Help - YouTube Stories for Creators
Information on Stories and how to create them.
Link missing here or found errors? Improve How-Tos