Once you install the two apps and link your accounts together, you'll see a Spotify icon within Waze, which lets you open up limited playback controls, playlists and the Spotify app. At the same time, from within Spotify, you can see Waze turning directions.
To keep your attention on the road, Waze has added a few new safety features. For one, Spotify playlists start automatically when Waze navigation begins, and to switch playlists, you have to stop the car. Nothing stops users from just switching over to Spotify the regular way, but if your music is already playing, it might help you resist the temptation.
As we mentioned before, it's a bit odd that Waze, a Google company, is integrating with Spotify rather than its own Play Music service (or Apple Music, now that it's on iOS). Such integration between more mapping and music apps would be great, and if all of that could be voice-controlled, then we might have something. For now, the Spotify and Waze integration should be rolling out now, so you should see it within the next few days.