The story map will be initially shared internally and eventually shared with the public.
To share a story map into a group, it is best to go to My Content in ArcGIS Online, click the check box next to your story map and then click the Share button. The dialog that appears will list the groups you have permission to share the story into. Help topic on that.
Don't launch the Story Map Cascade Builder: that lets you configure/edit your story map, and lets you share it either to your organization or everyone, but in the Builder you can't share the story map to a group. You also can't share a story map to a group via My Stories.
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?
I already have a story map created I am trying to share it in my internal group and it isn't showing up to others included in the group when shared. Since it is a web app it is confusing that it would give me the option to configure it with web app options.
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