This is a question I’ve been asked twice in the past week. And I concede that WordPress (the software that this blog uses) is not particularly intuitive in that regard.
If you wish to comment on a post, click the Comment word at the bottom of the post. IMHO this is why it isn’t intuitive. At times the “button” will say No Comments, and at other times it’ll be something like 1 Comment or 2 Comments (or however many comments exist for that post).
Click it and you’ll come to the log in link, or if there are already some comments, go to the bottom and you’ll see the prompt to the log in link there. Once you get logged in, you can comment to your hearts content. Also, once logged in, you can comment on any other post without additional hassle.
The reason for all this is to help control idiots, spam and bots. That’s the way the software is set up and I have no control over that.
So, comment away folks. Really, it took far more time for you to read this than to log in and comment.
P.S. I got a chuckle when I was about to post this and the WordPress spell checker kicked in. The word that was flagged as misspelled was WordPress.