First of all, it's important that your phone/tablet is on the same WIFI network as your Sonos speakers. The app automatically detects Sonos rooms when it runs for the first time (see this video of the introduction) and when you want to assign a command to a room. The rooms have to be set up with the Sonos app beforehand.
Controlling your speakers is very easy. You can just choose a gesture, a function and the appropriate Sonos room and you're ready to go! This video shows it in detail:
There's also a touchpad preset that you can use. Look here for more information on that.