I've never used the buddy list, but I understand it's a way to send private messages to a number of TCS members at the same time.
To edit your buddy list, go up to the buttons that are just under the Royal Canin ad. Click on "Options." On that page, you will find a row of options that includes "Edit Buddy List."
You can add or delete names to it (in addition to just clicking on "buddy" under any TCS member post if you want to include them as a "buddy." That automatically adds them to your list).
I believe you can then utilize Private Messages to send to your buddy list.
I am going to go ahead and move this post to The Cat Lounge as it is a general question and not directly related to S.O.S.
Hope this helped! And maybe someone will chime in that knows more about this than I do.