@chloeab1 has it right.
Discourse supports a custom flavor of Markdown. Markdown is a group of languages (or refers to any language) which uses plain-text special syntax to produce formatting when parsed. Discourse’s flavor of Markdown supports all of the basic syntax like *italic*
italic, **bold**
bold, ~~strikethrough~~
strikethrough, etc.
If you want to include a separator line you can use ***
or ---
after an empty line. Like below:
Take a look at this post for advanced formatting: