1. Click on "Activities" on the Navbar inside your course.
2. Select "Discussions" from the drop down menu.
3. Your discussions list will appear and choose the discussion you wish to post too. In this example, I only have one but you may see many more.
4. Click "Start a New Thread" if you are posting your initial post OR click on the name of the thread if you are posting a reply.
5. To post a reply after clicking on the name of the thread (shown above in #4), click "Reply to Thread".
6. Type in your reply (#1) and click "Post" (#2) when done.