Let’s say I start a journal, which I did, as a new topic. A week later, I create journal entry 2 as a reply to my first journal entry.
Then a week later, I want to do journal entry number three. Should #3 be a reply to journal entry one or journal entry 2?
I’m not familiar with this forum interface, but I could see that if there is indenting, it might make sense to have all new journal entries be replies to the first journal entry, to avoid runaway indenting.
Either way should be just fine. Discourse threads are linear—all posts appear one after another. There isn’t any of what you refer to as indenting, though you can choose as necessary to quote previous posts in the thread to give context.
So it matters only very little if you reply to the original post or a later post. To quote the Discourse new user guide:
Discourse shows all posts in the order they are published. It does not make you chase down multiple threaded paths. However, it still gives you lots of ways to follow the context of conversations.
To reply to a specific post in a topic, clicking the grey Reply button at the end of each post and your reply is linked to that post.
If your reply is the next one published after the post you are replying to, this will appear next in chronological order
If yours is NOT next, then two things happen after your post is published:
Your post will include a new link in its header with an image to show what this is ‘in reply to’ - clicking this link displays that previous post for context next to your reply
The original post includes a count of replies at the bottom - clicking this link displays the content of the replies
That’s a pretty complete summary of what it means to reply to a specific post (as opposed to replying to the top-level topic.)