Is there a summary on how to format posts in the new forum? I only now learned how to tell it text is code. There’s still other things I don’t know how to do.
As noted in here that is pretty much it.
If you see something in another post you like and want to use it then just click on the edit icon (pencil) in the lower right of a post (may need to click ellipsis first) and look at the raw text, most of the time you can copy the formatting from there and it will work.
To get more advanced requires either knowing how to get some hand written HTML pass the Discourse checker which filters out most of the fun HTML, asking the admins to add features which is how I wound up as an admin (ref) and there are not many more features that we can add. The last option which we can not do with this site because of licencing is adding more plug-ins or custom plug-ins, unless of course you want to sponsor this site for a higher plan. 
How can I see the raw text if edit is not an option? I only get the option to see the text if I wrote it.
Glad you asked.
EDIT
Use the raw post button.
Older answer that is inferior to the above answer.
The URL for one of the earlier post is
https://swi-prolog.discourse.group/t/forum-formatting-references-markup-etc/2286/2
There is an alternative URL format that will reveal the raw text as entered.
https://swi-prolog.discourse.group/raw/2286/2
Older answer that is inferior to the above answer.
The solution is to have your trust level bumped up which I just did.
But that will only work with pages that are wiki, e.g. this
Try it now.
The other option is to use the developer mode of most Internet browsers by pressing F12 and then using the inspect option.