Use “markdown” to format your posts
If you click a link on the formatting bar when adding a post you’ll see some weird codes appear in the text. Take a look at the Daring Fireball Markdown Basics page to learn the markdown codes you can use or, better yet, look at the Markdown source of that page to learn by example. You will find it’s quick and easy once you get the hang of it. You can then draft your posts offline in a text editor, in email replies to notifications from the forum, or online in the forum.
Use “emoji” smileys to express your feelings 
More than 100 emoji images can be used to embellish your posts to express your feelings! To trigger emoji autocomplete, start typing a : colon then some characters.
Use @name to mention someone to make sure they see your post
Like on Twitter and Facebook, it is possible here to mention someone to get their attention and make sure they see your post. They will get a notification as soon as you save your post. To trigger it, type @ and then start typing their name or username. Discourse will autocomplete. So typing @tango will make sure I see it. You can also mention a group in the same way and it will automagically mention everyone in the group.
Upload pictures and attachments via the web
You can upload a picture or other attachment to embed in your post via the web. Just go find the URL and then select the “from the web” option after selecting “upload”. It will first embed the remote link while you edit and then later will go fetch the file to keep a local, permanent copy.
Authorized filename extensions are jpg, jpeg, png, gif
Embed a preview of another forum post
You can easily reference another post by just grabbing the URL from there (look for the link button under the post) and inserting it on a line by itself and it will automagically be presented like the example below.
Embed a video in your post.
Just stick the URL of a youtube or vimeo video on a line by itself and it will automatically be embedded in your post. This link https://www.youtube.com/watch?v=KMU0tzLwhbE on its own line produces this:
https://www.youtube.com/watch?v=KMU0tzLwhbE
Embed an anonymous poll in your post
Source: How should we implement polls? - #40 by riking - feature - Discourse Meta
Make your topic title start with "Poll: " and include a list in your post. The first list will be used.
Intro text
- Some list
- Some list con’t