A family of Microsoft products that enable users to capture, organize, and reuse notes electronically.
In the "original" OneNote for Windows tags have been implemented with the purpose to
- Mark any object like paragraphs or images with a special symbol to "emphasize" or categorize it.
- In addition a (rather weak) search "report" function has been added (the one you showed in your screenshot) to output a grouped list of tagged objects.
Somehow the development has stopped there. For example there is no way to add a certain tag to a search phrase (like in Evernote). It remained that way from Onenote 2003 to the current 2016.
With the release of additional OneNote versions for Mac, iOS, Android and the Win 10 app the developers included the ability to add preconfigured tags (not custom created tags), but left out any search or summary function (so far?).
So from this point the link Tina Chen posted, is correct, but of course not that helpful as the linked article does not make clear what you can NOT do with tags on OneNote for MacOS.
As far as I know the whole tagging system is currently under review by the developers, so maybe we can expect some improvements in future versions.
In the meantime I would suggest to add a vote here:
https://onenote.uservoice.com/forums/327165-onenote-for-mac/suggestions/15330843-tags