If you wish to be notified by email when there is a new topic in a specific forum, simply go to that forum and click on "Subscribe for new topics" at the top.  That link will then change to "unsubscribe", allowing you to stop notifications at any time.

If you wish to be notified by email when there is a new reply on a specific topic, simply go to that topic and click on "Subscribe for new topics" at the top.   That link will then change to "unsubscribe", allowing you to stop notifications at any time.

In both of the above cases, you will receive an email asking you to confirm your subscription, just follow the instructions!