Help CenterTags are only available on Topics since it is Topics which hold the content visible to guests. You can’t set Tags on the Categories or Subcategories, if you add some Topics to a section then you will be able to give them Tags.
See this article for more details on the Category, Subcategory and Topic structure of Touch Stay: Categories, Subcategories and Topics explained
Note that any section without any Topics won’t show in your guide. They must have Topics of content active for the section to show in the guest view.