Use the "Edit" button at the top right of the main page to get started. Change the welcome message at the top to add the course name as well as your name.

Visit the "Course Info", "Instructor Contact", and other pages to fill in some details about your course for students to see.

Add any important messages you want students to see when they come into the Forum under the "Announcements" heading. You can also note any important discussions you want students to participate in under "Current Discussion Topics".

Remember, you can customize the information here as much as you like: add new pages, delete the links to ones you don't need, and lots more. Look at Organizing your Forum for some other ideas.