Open up your Music app.
See the menu bar at the bottom? (Just below this caption box)
Choose the Radio icon.
In the Itunes Radio menu, you can: 1) Choose one preset radio station 2) Create your own radio station
1) Choosing a preset Radio station. (I chose iTunes Top 100: Alternative, just as an example)
2) Creating your own Radio station. Here you can select some genres, or maybe include specific artists, songs or genres.
Im looking for Chuck Berry, just as an example.
Now iTunes chose some artists and songs based on my selection, and generated a new Radio station that I might like.
There's also another way to create a Radio station.
You can create Radio stations based on what you're listening right now.
See? Click that Create button to start another Radio station.