Cepas,
Subscribing is when you add a thread to your "list" so you will get notifications and have easy access to favorites. It's kind of like a favorites list. Whenever you post on a thread, you are automatically subscribed to it. You do not have to post though, you can simply go up to Thread Tools at the top of the thread posts and click on it, then click on subscribe to this thread.
Later, you can visit your favorite threads by going to Quick Links in the Disboards top bar. After you click Quick Links, click on Subscribed Threads. Once there you can decide if you want notification of any new posts that people make sent to your e-mail. I am subscribed to many, but the e-mails do not come for some reason anymore... So I simply go to my Subscribed Threads (under Quick Links) and click on the ones I am interested in. Go ahead and try it yourself now, any threads you have posted on will be in your own list of Subscribed Threads. Whcih, at the moment, will only be this thread!!
Easy for you to try this feature and easy to delete them when you no longer are interested in a particular thread.
Hope this is not too confusing!!