In order to comment, you must register. Go to the “Meta” menu on the right hand side and hit the button that says “register” and a dialog will come up asking for your username and email address. A temporary password will be sent to the email address you provide. Once you receive it, come back and log in. At that point, you can change your password to anything you want. You will not, however, be able to change your username, so give it some thought.