@bigstick:
^ gotta upload your image somewhere, like imgur.com, then grab the url of the image (will look something like
https://imgur.com/VKHliXDh.jpg) and paste THAT between the [ i m g ] [ / i m g ] tags.
pro-tip: you can add a letter before the .jpg (
https://imgur.com/VKHliXDh.jpg) to override the size, if the image is too big. (s = small, m = medium, l = large, h = huge)