|First, choose an identity.|
Using the anonymous setting means you don't have to have an account with any of the listed services in order to leave a comment. However, if you use one of the accounts in the drop-down list, it's possible to have your name link to your account so people can contact you.
Because spam is such a problem on blogs and Web site comment forums, devices are in place to prevent mass spam attacks, and you will be asked to prove you are not a spam robot. You will be presented with a symbol (like a circle or square, for example) to click, or letters or numbers to type into a box. This is called a CAPTCHA (an acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart"). Presumably, only humans, and not spam-spewing robots, can perform these tasks. (In the case of letters/numbers, they can sometimes be hard to read. There is a curved arrow to click on to get a different set of letters/numbers. Click on it until you get a set that you like.)
Once you compose your comment, you can preview the comment before submitting it. If you approve of what you see, publish your comment for all of us to read.
It takes much longer to read about commenting then actually doing it — it's easy!