I have found it a little effortful to make the Discourse terminology and structure second nature. The basic structure is
Categories, containing
Topics, containing
Posts (the First Post is the one that created the topic, and the rest are replies.)
Categories can also be nested, at least two deep - useful on larger sites.
Whether you reply to the first post, or the last, or any one in between, is all the same I think. (Posts are linear, and don’t have tree structure like on a mailing list.)
Tags are an optional complement to categories. They are probably best used sparingly, if needed, for things that frequently cross-cut the categories.
Users belong to one or more Groups (which we don’t use much so I have hidden the menu item). They have a Trust Level which gradually increases from 0 and unlocks more powers as they use the site more.
Categories are the equivalent of different Forums or Rooms of Matrix. I would suggest the following Categories to begin with:
Categories for PTA software:
ledger-cli
hledger
beancount
text editors
Categories for Double Entry Accouting and Acounting discussion:
accounting
General categories:
Site or Meta (for discourse/forum related topics)
¿private category for site admins?
It is also interesting to not have too many categories, just the required ones. Because too may categories make difficult to assign topics to one category. Or then moderators have to move topics from one category to another one.