At the beginning of the AEM Headless Content Author Journey the Introduction covered the basic concepts and terminology relevant to authoring for headless.
In the previous step you were introduced to the use of references for Headless CMS Authoring. You learned what sorts of references are available, and what are their purposes: Content References, Asset/Media References, and Fragment References.
This article builds on these so you understand how to use metadata and tagging to author your own content for your AEM headless project.
You can add metadata and tags from the right panel of the Content Fragment Editor:
Now you can put all this knowledge to use and start creating Content Fragments for your project.