There are 2 types of credits within your Boost Collective account.
Promo credits are used for the Playlist Promotion tool only, and are earned whenever your rank increases (eg. from Recruit to Major).
Regular credits (seen as '10 Credits' above) are used for everything else in the 'Armory' section of your dashboard. Regular credits are earned for every song you distribute through Boost Collecitve.
You can see how many credits of each type you have on the top right of your dashboard: