If I understood correctly, you should see four rooms/zones in the Sonos S2 app. Add Spotify to Content Services in the Sonos app. Then access first card/zone, do a search from Spotify or select from your Spotify library in the Sonos app and add the tracks to the queue for that zone. Press play. 
 

In the System Controls (swipe up from bottom), select second card/zone, do a search from Spotify etc. and add to queue for that. Repeat for the other zones similarly.  

You’ll have individual queue for those zones that you then clear or add more tracks etc.

Swipe from the bottom to see the System Controls UI that shows the zones and you can press play/pause on that UI individually. Tap on the card to select that zone, the control minimizes to the bottom. Tap on it to open just that zone. You can then see the UI elements for queue and other controls for that zone (shuffle, repeat etc.)

Read more in the user guide:
https://www.sonos.com/en-us/guides/sonosapp

”Select a card to change which output the app is targeting. Outputs are displayed as groups, home theaters, stereo pairs, portables”