When the Minx Air is connected to your home network, when you open iTunes on your computer, or your Music app on an iPad or iPod, you will see the AirPlay logo.
Tap the AirPlay logo and you will be able to select the Minx Air as the playback device. Wait a few seconds for music to start playing before you adjust volume.
In the update to iOS7, Apple moved the native audio source option from the iTunes/Music app to the "quick pull” menu. It will depend on the individual app as to whether it still has the icon in the corner (Pandora obviously does), but ultimately it’s not necessary anymore, as the quick pull menu will override it and send audio to whatever speaker you’ve told it to there.