9hb,
it's actually a pretty easy two-step process; paring it down from the above gamage of verbiage:

1) Subscribing to a Topic
Enter the Topic and Select "Add Topic to your Watched Topics" option from the "Topic Options" dropdown. [this option can be found at the top of any thread]
2) Toggling the Default "EMail Watchedlist" Options
Select "My Preferences" from the "My Stuff" dropdown. From here you can manage the "By default should anything added to your Watch Lists be emailed to you?" option.