To show a collection of related stories at the bottom of your embed, simply select Show related through the embed options as shown here:
Once you've selected Show Related through the embed options, you'll see four additional options to customize your related stories:
First you'll see a dropdown of collections to choose from. Select which collection you'd like to feature in your related stories here:
If you want to create a new collection for related stories, create the collection first and then return to your story's embed options customization.
For a refresher on how to create collections, visit this page.
If you're running a UGC campaign and want to include a "Share Your Story" call-to-action, select this option.
To customize the text that introduces the related stories section, select this option and enter your desired text:
To maintain the same settings for your related stories that apply to your embeds, select this option.