Hi, generally speaking if you're approaching a regular person you would use "Du" or "Dig" as mentioned above it is only when addressing Royalty and old people we would use "De" as it is very formal and would be considered rather strange when used in a normal conversation. Do note "Due" means they as well so if you are referring to a e.g. a couple you would say "De" e.g. They are nice; De er søde.