Deezer is hoping you'll use the radio app with its main streaming app. You can "like" any song that hear on the radio, and it'll be added to your "favorite tracks" library within the app. The app will then transfer the liked songs to the "My Music" section of the Deezer streaming app.
Deezer is far from the first app to offer radio stations, as the now defunct Rdio, along with iHeartRadio, Pandora, Apple and others have done so before. However, Radio by Deezer seems to have one of the widest station selections, and it's a smart idea to integrate it with its paid or ad-served streaming app. Radio by Deezer is subscription-free, but as mentioned, it's only available in the UK and only on Android for now.
Updated 1/16/2019 8:47 AM: The post has been updated to indicate that Radio by Deezer is in a full release, not beta, in the UK on Android.