To do this:
1. Make sure you are logged in.
2. Go to the board you want to bookmark.
3. Next to the board title you will see "Add this board to your favorites". Click that.
4. To access your favorites click on "favorite boards" next to where it says "Welcome yourname". You will get a popup window of all the boards in your favorites and the boards you have recently visited. You have the option to add the recently visited boards to your favorites.
A couple neat things about the favorites: the number of new messages on the board are shown and the number of new messages to *you* is shown (i.e. somebody replied to your message).
So do this quickly now before you forget it. It only takes a second and isn't as hard as it sounds.