Markdown is just code you put into your post to format it.

You can do bold, italic

Headers

Of

Different

Sizes

• Unordered
  • Lists

1. Ordered
   • lists

And lots more. Just click on the "Styling with Markdown is supported" link when you are entering your post on the steemit website. It's a good practice to use your word processor to write, then format on this site. Formatting makes your article easier to read,