As a member of the forum, you can use the notifier feature to get email alerts on new topics and reply to topics.
To get a notifier on new topics on a specific, open the index page for the board and click the notify button right above the list of topics (threads).
If you want to be notified of replies to a specific topic, open the thread and do the same, click the notifier button.
On your profile page in the forum, you can change settings, or oversee the topics and boards you are currently receiving notifications for. You can choose to receive notifications with the post itself in the email (but please don't reply to these emails.) The settings is under "Notifications and Email" in your profile menu.