Bookmarking only marks where you are up to in a thread. When you click on the thread you will go to your bookmark and not have to scroll through from the beginning. Watching is a list of threads that you want to find easily. If you have made a comment on a thread these will be under "I'm on"
op, bookmark where you read up to/ the current end of thread. then scroll up and click orange box, watch this thread. then when you want to find them again, under Gransnet forums heading, click on, watching. you should be able to find them.