Within Slight Run, Markdown is used for "Documentation" entries, whether on a whole app or dataset, or on individual variables and columns. Each of these also comes with a simpler "Description" entry, which only takes plain text and a lower character limit.
We don't yet have our own guide up. For now, The Markdown Guide's basic syntax page is a great starting point. For any markdown block on our site, you should generally be able to type
/ to bring up formatting options.