See my answer to PA.
He asked the same thing.
When you are on the main Forum page click on the unread content button. It will list the treads with new posts since your last visit.
Beside each of the threads there will be a gold star, or gold dot, if you click on those it will take you the the first unread post ... should be where you left off.
As shrader pointed out there will also be a blue line (like on hockey ice) that will show that you have read the posts above that blue line.
This is a recording ...
Sabres Fan in NS's post in What happened to the calendar on the main page? was marked as the answer