I bet most have noticed they little numbers that just keep climbing on the topic tabs. That is telling you how many unread items are in each area.
If you want to MARK ALL THREADS AS READ and reset this so that you can stay on top of all the new post and articles just go to whatever section that you want to perform this action and hit the little checkmark in the upper right hand corner. Remember you will have to do it in each section that you want to reset.
Here is a picture of the place to click to MARK ALL READ.