Similarly to assigning jukebox credits to a song to queue up its play, applying Play Credits to a song in your Radio Airplay account is what actually queues up the song for that many plays on Jango Radio stations.
To apply your Play Credits, go to the PLAY CREDITS tab in your account's top menu and click on USE CREDITS. Similarly you can go to ARTIST CONTENT and SONGS to get to the same page.
If you have available credits for use they'll be marked as Play Credits Unapplied. If you have any credits currently Applied to your song(s) they'll also appear totalled in this section on the top right of this page.
How To Apply Credits: Hover over "Apply" next to a particular song on your list and the increments you can apply will appear. Choose one of those amounts to place that many of your unapplied credits to the song. Once plays are applied, this is what will actually queue up the song for that many plays in the Jango Radio artist stations you've chosen to reach listeners in.
Once credits are applied to a song, plays will begin automatically within a few hours. You don't have to do anything else. As the new play credits are used, your Radio Airplay account will update with information about those new Plays and Listeners. Each used Play Credit will correlate with a new Play and Recent Listener in your account information.