Not sure what you mean by “meta-information” or sub-categories. There are so many ways to interpret those words.
Categories are pretty straightforward: add the “internal link” to the category in question. If a category is part of another category, as in the Category:2018 Meetings, which is part of Category:Meetings, adding a page to the category’s category makes it a member of the subcategory.
Anyway. This can get hairy quickly…
As for what I suspect you mean by “meta-information”, I suspect you mean hidden keywords and phrases such that a page returns on a search even if the words used are not displayed on the page, but fit the intention of the search. Embed hidden phrases using the comments tags, as employed on the Metal Suppliers page
<!-- Please use Wiki-style mark-up, not HTML, unless there is no other way to do it. -->
<!-- See https://www.mediawiki.org/wiki/Help:Formatting -->
These words will be indexed and searchable, as much as Mediawiki ever is, despite not displaying in the read pane.
Of course, maybe I completely misunderstand the intent…