The Songza integration works just as you might expect. You start off by choosing what you're doing - working, driving, taking an autumn stroll - from a list that will change based on the time of day. Then, you choose the type of music you want to hear within that category. The idea is that what you're doing feeds into the tempo and energy level of the music, then you choose the genre you want. So, within the "Autumn stroll" category, you have options for "a soulful stroll", "an acoustic excursion", "a hip hop stride", and more. Google is saying that this is only available for subscribers, meaning you'll have to be paying for All Access in order to get the Songza features.
The update also reorganizes things a bit. One change we love is that the recommended music and playlists have been separated from your "recent activity" rather than having the two mixed together. Otherwise, the only real changes are to the UI with the new Material design look and animations.
The update will be rolling out to everyone through the Google Play Store; but, if you're impatient, Android Police has the APK for manual download at the source.