From the frontpage of this message board, you will see there are certain topics. You clicked on the how do I... topic to get here for example.
Choose the topic you want to discuss and click on it. After doing that, you will see a list of discussions that people have already started. You can either go into those already started discussions and click 'post reply'. Then simply type your reply and press submit.
OR... if you want to create your own discussion, click on "new thread" when in a section of the message board, and you can start your very own!