raichu...when you signed up to AB there should be a box to tick saying you wish to be informed of any answers to threads you are involved in .
Subscribe to thread means just click on it ..it's above ..left hand side and then you can go to your profile and check how a thread is going which you are involved in.
Have a look at the tutorial which can explain it better than me !!
Welcome to AB.
http://www.theanswerbank.co.uk/ABTutorial.html
Anything you want to know is at the bottom of the page
Click on tutorial or Faqs .