1. Locate the discussion board. The link to the discussion board is usually accessible on your course menu.
2. On the discussion board page, click the name of the forum to which you would like to subscribe.
3. In the discussion forum, click Subscribe on the action bar.
4. When you have successfully subscribed, a green success message appears.
5. If you would like to unsubscribe from a forum, click Unsubscribe on the action bar.
6. When you have successfully unsubscribed, a green success message appears.
https://en-us.help.blackboard.com/Learn/9.1_2014_04/Student/090_Tools/Discussion_Board/010_Forums