Go explore!
Nabes will show you the names of neighborhoods as you discover them, and keep track of your history. You can even see how you rank against all other players in the Leaderboard screen.

Just sign up, then the app will track location changes and do its thing. You can see your Current location or look at History by clicking the tabs at the bottom of the screen.

When you discover a hood you'll be able to see its shape on the map.

Note:
You can only discover a new neighborhood when going relatively slow. For example, driving around on a freeway will not let you register new hoods.