In some countries PROs are called copyright collectives or copyright collecting agencies.

*Thank you wikipedia

Basically, you join your local PRO/copyright collection agency or patant place or whatever, and every song your write and submit is registered on this huge catolog of songs.
I'm talking the Matrix of all that is Holy here, like, the ultimate song book.
You register, get a CAD number, tell them your bank account details and all that, you become a member. - If you have a stage name, then you can register that and they will generate a whole new CAD number for that and your original name and original CAD will act as the ultimate, and all payments for all other registered CADs, will see your share paid back to your original name and CAD, which is just your name.

In the UK, it's called PRS and because of some deal that was signed way back in the days of old; I choose who I want to represent me in the US, and... There are like 4 options... ASCAP, BMI, SESAC and I don't know.

I usally just do ASCAP, but every ther country in the world I'm with PRS.
BMI, in America, I think with BMI and SESAC, one of them is just for musicals and the other is for radio, or, something, idk. but, I just choose ASCAP anyway as, that's the one I prefer. - Not that it matters I haven't seen one payment yet.