bold
italics
a link to the markdown tutorial
reference links allow you to write a url once to be referenced by multiple links on a page:
Here's [a link to something else][another place].
Here's [yet another link][another-link].
And now back to [the first link][another place].
[another place]: www.github.com
[another-link]: www.google.com
{from http://www.markdowntutorial.com/lesson/3/}
the tutorial also describes how to inlcude images, blockquotes, and lists
paragraphs are formatted by inserting two spaces at the end of each line (newline vs new paragraph)
If there were not two spaces at the end of the previous line, this line would not be a separate line.