No, not that kind of discourse. The discourse that I'm talking about has a capital D and powers the brand-new AppleTalk Australia forums. It's a little different to the forums that you might be used to, but don't panic — everything still works very similarly to what you're used to, with a few new added perks. Most of it is pretty self-explanatory and fairly intuitive. You can find your way around by just having a wander and clicking around (don't worry, you have to click pretty hard to break anything), but I've compiled a few basic tips in addition to the ones you get when you sign up for the forums.
Topics are the new threads, categories are the new forums
What you used to know as threads in other forum software are now referred to as topics, and similarly, while other forum software separated discussion topics into forums and sub-forums, categories keep related topics together.
The main page (which, by default, shows every recent topic) can be customised to show only the categories you're interested in, and if you want, you can still browse the discussions by category. If you want to see a more "traditional" forum structure, use the Categories tab at the top. But I recommend sticking with Latest - you'll get used to it quickly.
Creating and replying to threads and posts
Discourse uses Markdown to compose posts, which is why you see two panes when composing a post. The pane on the left is your run-of-the-mill plain text editor, and the one on the right is how your content will turn out. You can use bbcode if you're already familiar with that (and there are buttons you can press to create links, lists, or to make your text italic or bold) but Markdown is the way to go.
New to Markdown? There's a handy reference guide right over here.
Want to create a poll? Just make sure your new topic title begins with "Poll:" and make a list at the top of the first post. And if you want to close the poll, use the Close Poll button.
One of the biggest problems with other forum software is the need to upload images to a separate service. Discourse is different in that you can simply attach images to your post by dragging them to the post editor, where they'll be automatically uploaded and inserted into your post. Now you can show everyone the exact error message you're seeing, although you should still blank out any personal info such as phone numbers, emails addresses, and serial numbers if you're feeling paranoid.
One of the most often-requested features of other forum software is some way to "like' posts, to show the poster what they said was insightful, funny, or that you agreed with what they said. Unfortunately, that wasn't possible with most other forum software without some third-party plugin, but I'm pleased to announce Discourse has built-in support for liking right out of the box, so like away!
If you have ever "reported" a post in other forum software, flags will be familiar to you. Flagging a post gives you a number of options, including marking it as inappropriate, spam, off-topic, or even bringing it to the attention of the original poster. Most of the options notify the moderation and admin team, so don't hesitate to hit the flag button on something that looks like it doesn't belong.
Pinned topics work a little different in Discourse. You can clear a pinned topic any time you like once you've read it, but that just un-pins the topic for yourself.
If you want to come back to a thread later, bookmark it. You can bookmark individual posts, too. A red bookmark means you've read posts up to that point, a blue bookmark means you've manually bookmarked that post for later (accessible via your profile page).
Reply as new topic
If a post in a discussion thread has reminded you about an issue you've been having or something that you've wanted to discuss, but doesn't fit into the main theme of the topic, then this is the button for you. Simply put, it lets you take the conversation in a different direction without affecting the topic at hand — it's great for taking things on a different tangent without interrupting the flow of the current thread.
Discourse uses a trust level system. Threads you read, reply to, and create yourself will contribute to how much you're trusted. These trust levels grant additional privileges, including the ability to deal with flagged posts, spam, and so on. If you want to read more about the trust levels, check out the post on Meta here.
I'll update this thread if I think of any other new stuff that's worth knowing about, but please feel free to post below if there was some way of using other forum software that you enjoyed and aren't sure exists in Discourse. (There probably is, it just might be in a different place than you're used to.)