You can register for updates from any category (i.e. all elementary articles) by clicking that box in my account :: subscriptions :: category. Once subscribed, this will send you an email whenever new content is posted to that category.

If you are only interested in subscribing to a particular story (thread), click on either the title of the story or the read more tag at the bottom of the listing. At the end of the complete article you'll find a subscribe post link. If you click that, you will be sent comment updates to your email address. This is only available if the author has comments enabled.