I don't mean to patronise or to insult peoples intelligence but I feel I need to explain the two functions because I don't believe they are labelled correctly. Unfortunately, due to the limited space in the left-hand column, any other description would be too long (unless someone has a suggestion?)
- Unread Posts
This link searches through all the forums and finds all topics that contain posts you haven't yet read. Any topics found are listed in chronological order with the most recently updated topic at the top of the list. Click on the little orange box next to the topic title to take you straight to the first unread post in the topic in question. - New Posts
This link takes all topics that have been newly created since you last logged in and lists them in chronological order, with the most recently updated at the top. This list of topics may contain unread posts in some topics but crucially it will not show you any older topics that may have been updated whilst you have been offline.
I hope that might make things clearer as to what the two functions do. Of course, if anyone has any questions then just ask!