It's the quasi html format used on Steemit to tweak out your posts with h1, h2, h3, headings, bold, italics, quotations, inserting images etc.

Always good to have a heading inside your post to make it standout and also the other tools.. very easy to use. im sure there are plenty of posts about using the markdown styling tool. if ya need help with it let me know.. The price of STEEM and SBD - thru the roof!! Lets hope it stands.. :) my wallet went from $800 to $2300 in a little over a week