Hi Sharla
A Cascade story map is a web app. So to make a Story Map Cascade you can go to the page about the app and click the Build button: Story Map Cascade | Story Maps
In a Cascade you can include existing ArcGIS web maps that you or others have authored.
Once you've created and shared your story publicly, you can promote it ito your audience in the same way you'd promote any other web resource. For example you can add a link to your story into the appropriate web page on your organization's website, link to it from a blog post, tweet it, add it to an email newsletter, etc.
Hope that helps?
Rupert