Hey
Everyone can use subscriptions. Basically it's a way to track (it used to be called Tracking) the threads or boards you visit so that they show up when you click your User CP. It's very useful if you visit punctual threads on boards and don't want to look for them each time you visit Fan Forum.
You can also have email notifications sent to you, that depends on what you decide. Just click on "Subscribe to this thread" (which is at the end of the page) or "Subscribe to this forum" (which is at the top of the page) and you'll be able to play with it a little bit