Starting in Drupal 4.x, I think, Drupal Core had a capability for a module to provide 1 help topic (which we now in Drupal 8 call a "module overview"), and to add a small amount (typically) of help text at the top of one or more admin pages.
New in Drupal 8, modules and themes have the capability of also providing "tours", which are guided tours of their administrative pages, via the core Tour module.
And there's a group of us that are also working on a module for Drupal Core that would allow modules and themes to provide additional help topics, organized by task instead of just 1 module overview; site builders would also be able to write topics.
So... I just wanted to bring all of this to the attention of this Documentation group, and also call for your participation! How you can help:
a) Right now, core only has a few tours. There's an issue where we are discussing what tours we need:
https://www.drupal.org/project/drupal/issues/1921152
So, you can go there and get in on that discussion.
b) Once some tours are decided on that should be created, you can participate in creating them -- there are child issues on that issue above for creating tours. Creating tours using just Drupal Core is not easy -- you'd need to create/edit a weird-looking config file. But there is a contributed module that you can use to create them in the admin user interface, and you don't need to be a programmer to do it:
https://www.drupal.org/project/tour_ui
I guess we need to write up some instructions on how to create tours... once we figure out which tours should be created.
c) The issue to create a topic-based help system in Core has a patch that needs reviewing and testing:
https://www.drupal.org/project/drupal/issues/2920309
And there are discussions going on about whether that system or some other type of system would be best, on this issue:
https://www.drupal.org/project/ideas/issues/2592487
Happy documenting!