SmartyStreets provides a street level validation and address suggestion service. With this integration enabled, street level look ups will be available from the admin's order edit screen and the customer's address book.
Make sure you associated your domain with your website Keys. https://smartystreets.com/docs/cloud/authentication#htmlkeys
Copies these keys into Tools > Apps & Addons > SmartyStreets:
Zip code look ups are always available on these screens regardless of smartystreet integration. Typing a valid zip code and exiting will autocomplete the city and state.