I'm not 100% sure, but I think it'll just work automatically through Store on the Xbox One. The game will just appear there and you can Manage/Install it the same as any other game/app/addon that you add to the Store remotely. (I think codes are normally used for ex-retail purchases, e.g. if you get a game or extension pack bundled in with an accessory or console :- one of the steering wheels is bundled with Project Cars I think, and Sainsburys had the Xbox One with Assassins Creed Black Flag/Unity on a code card. That's the one I have.)
Slightly guessy, but I'm usually right.
