Locate the message board:

1: choose to post a reply to an existing message or  2: start a new discussion

1
Locate the correct discussion. Click on it. Select  Reply

A new window appears, Compose your message then click send. (the new window disappears and the message board refreshes your reply is now visible

2
Click start a new discussion

After the new window appears, type in the subject for your message. Compose your message then click send. The new window disappears and the message board refreshes your reply is now visible.