Here's a few quick steps to follow certain posts and receive notifications:
1) Go to the course discussion forum page
2) At the bottom on the page, click the check box next to "Receive Updates"
This will enable you to receive email updates. To choose a particular thread to follow, click the grayed out star in the upper right hand corner of any topic. It will turn blue — now you are following this thread.
You can read more about this topic in our Learner documentation.