I see a bunch of comments on someone else's answer to several questions and I'd like to add one but I don't see how. I can provide my own answer, but all I really want to do is add a little bit to someone else's.
You need at least 50 rep before you can add a comment. (Although you are always able to comment on your own questions & answers.) Once you have 50 rep, an "add comment" link will appear underneath each question and answer.
I see you answered a bunch of questions quite recently, You'll get 50 rep pretty quickly once people start voting on them.