1) Choose a post, click on it, and scroll to the bottom.
2) Click "New User? Here's what to do".
3) Fill in the comment, choose a username and password (the one you want to use for your eventual comment account), and hit submit.
4) Wait 24 hours.
5-37) Refresh the page to see if your comment shows up. If it hasn't within a day or two, repeat on a different post with a slightly better comment.