Open the Radio tab and you can browse thousands of live stations by country, or search for one by name. The list comes from radio-browser.info, a free community directory of internet radio.
What happens when you tap
The station's own stream starts playing, like any other internet radio app. Because it's a live stream, it uses your connection, so keep an eye on mobile data if you're not on Wi-Fi.
What gets contacted
When the app opens it asks the directory for stations for your region, and then the stations' own servers when you play one. That's the whole list for radio. Your music files aren't involved.
Not a TuneIn replacement
To be clear about scope: Audionix is a cassette deck that happens to have a radio, and it isn't trying to be a full radio service. You get a directory, a search and the ability to save a station as a cassette. That last part is the fun bit.
On iOS, which is coming soon, radio is the only part of Audionix at launch. On Android you get the full deck.