In order to comment, you need to enter two things: first, the comment itself, in the big comment field (I could probably have made that smaller, but I like long comments; none of this microcontent stuff for me).
And second, you need to enter the URL for comment submission on your own website. This is where your comment will actually be posted. This needs to be the exact URL (you can’t redirect it with a .htaccess, so I learned) and it needs to be able to accept a POST request.
Stephen, I kind of follow your explanation of ‘rcomments’, but the technical specifications are a bit beyond me. I just wonder how this differs from micropub clients?