To sign in: type your email address in the log in panel in the upper right corner of this page and click the Login button. Then click the Add Post link that displays below the log in panel. You'll be directed to a page where you can add a message to this page. Then just give your post a Title and type your message in the message box. When you're done typing, click the Submit Post button below the message box, and your're done.
You can also comment on someone else's post by clicking the Comments link in the lower right corner of any post.