How do I post to or reply on a discussion board?
Click on the Discussions button in your course.  Then click on the forum you wish to post in (note: be sure to click on the name of the forum, not the number under Unread Posts.  The number only shows you items you haven't seen yet!).

To create a new post within the forum, click on Create Thread.

You must create a subject (this is the name of the link others will click on to see your post).  Type your post in the Message area.  If you want to attach a document, use the Browse My Computer option in the Attachments section.  Hit submit when done.  Your post is now on the discussion board (note: if your instructor has turned on the "Moderated Posts" option, your instructor will have to approve the post before it will be public).

To reply to a post, open the post you want to reply to.  Click the Reply button.  (note: hovering over a post will bring up any other options your instructor has turned on, like in this case, the quote option is available).

Replying will fill in the subject line for you with RE: and the name of the original post.  Type your reply in the Message area.  If you'd like to attach a file in your response, you can using the Browse My Computer button in the Attach File area.  Hit submit when done.

Your reply will now be posted to the thread.