It goes in the Add Comment Box
At the end of the blog post, on the right hand side, you'll see a little printer icon then Permalink then Comment. Click on Comment and it will open up a box underneath (you'll have to scroll down) where it will say ADD COMMENT. Someone with MOD powers will have to approve it before it will appear. On the bottom left, it will then say 1 comment (or how many ever have been left).