you earn dj points by leveling up (1 every two level, 3 every 10 level)
then you can give these points to the song you want
when you are in the song shop :
the number shown in
2 is the number of dj points you have
Select the song you want and clic on the button under to give one more point to this song
the number of DJ point for a given song is shown in
3 1 shows you if the song is downloaded or not (blue circle equals : song already downloaded)
if you want to download a song you haven't, clic on button
4 (please note that even if the song is downloaded, you can only play it once it's unlock)