This plugin creates a toolbar that will let your visitors add some common html markup tags to their comments. This plugin does NOT provide buttons for ALL allowable html markup - just some easy (and safe) ones. What your visitor will get is a couple of buttons - delete (strike-through) or strong (bold) or em (italics) or "block quote" or link (if you edit a file), and red and green and blue - that they can use to 'dress up' their comment.
Note that if you want to allow links in comments you will need to (a) edit one of the files in your installation and (b) get my Turing Test plugin to stop the spammers from assaulting you.