To add a message you first have to register. Click Sign In - no account - then choose a username and password. Also enter your e-mail address. Then click on Discussions, and you can either add a comment to someones message or start a new Discussion topic. Click the smilies (emoticons) to add them to your message

You can now also get email notification when someone replies or posts a message. If you click on ‘control panel’ up on the right of the masthead, a box should open with various obscure options in it. The bit you want is ‘notification’: if you’re reading a discussion, there will be a link there that lets you subscribe to that discussion. If you’re on the main discussions page, it’ll let you subscribe to the whole thing, so you get a message whenever anyone posts anything.

I’m not sure if this actually works, but if not it will soon.