You need to choose one of the providers in the GeocodingProvider ENUM (currently Google, Geocodio, LocationIQ, or MapQuest), and pass that into the geocode / reverse geocode action along with an API key from them, and either the Latitude / Longitude for a reverse geocode, or an address as a String for geocode.
These make an API call to the provider you selected, and will return the address as a String for a reverse geocode action, or a Position object for a geocode action.
Hope this helps.