Click on compose in the left frame. Then choose Edit and Paste from the Netscape Browser window. That will put your text inside the message box. If you know how to code html manually, then you can tag the text in the message with anything that works in the body of an html page. You can also copy and paste the html from an editor.
Anonymous postings are exactly that - anonymous.
Don't abuse the privilege. If your professor has added the homepage tool, you can create your own web page. Clicking on the homepages icon will take you to a page with a list of student names in the left frame. You can view any user's homepage in the left frame by following its hyperlink. To customize your own page, click on your name.