A TamaGuide or Admin has to pin it, if it has good info or great advice one of them will decide to pin it. It will auotmatically say "Pinned" when one of them pin it, so there's no need to type Pinned.
Well, once a month, Admin picks a new TamaGuide to moderate the site. To become a TamaGuide, you have to be an experienced TamaTalk user that helps new people and answers questions. You also have to be very active on the site.