There are 2 ways you can add a board to your My Boards list:
1. Directly from the Message Board you want to add
This is probably the easiest way. If you are already on the board you want to add, just click the "Add To My Boards" link appearing in the upper right hand of the main message board page.
NOTE: Once you have clicked "Add To My Boards", the link will disappear.
2. From your My Boards page
Open My Boards and click the "Add New Board" link in the upper right hand corner.
Then in the box that pops up, search by symbol or company name for a stock-specific board, or by Group name to add a member-moderated Group board, select the board you want from the results list and click Add Selected Boards.
From the Message Board you want to add