Instructions for Subscribing to Threads
 

If you want to subscribe to threads, you have 2 options:

Firstly, you can do it on a thread by thread basis
When you reply to a thread, just below the Submit Reply button, there is a section entitled Additional Options. The third option down is Thread Subscription.

The default setting is Do Not Subscribe.

Other options are:
1) No email notification (allows you to subscribe but doesn't send you email alerts. You can view the list of threads you've subscribed to by going to your Profile and clicking on List Subscriptions in the Subscribed Threads section)
2) Instant email notification
3) Daily email notification
4) Weekly email notification

Secondly, you can edit your profile settings so that you are alerted for all threads you start or participate in
Click on the Private Messages link in the top right hand corner of the Forum. You'll see your profile details running down the left hand side of the page. Click on Edit Options in the Settings & Options section and then update the Default Thread Subscription Mode (fourth section down). The same options as above apply.