If this has been discussed I haven't found a really all inclusive thread that explains. If it has and you have the link please direct me so I can unravel the mysteries of the lingo

Sync fee = This is what an end user pays for the right to be able to place an artists music to visual media.
So in a typical library deal where the sync is paid through the PRO and is split 50/50 that is talking about the payout for the song placing in film/tv.
Back End (no comments from the peanut gallery) = This is the revenue that is generated when a song is used on an ongoing basis in continual programming.
I assume this is also paid out through the PRO, and is for instances where you song might be playing in a show that is used after the initial sync fee is paid.
What I find confusing is; writer's and publisher's share. I don't understand how this is implemented. So when a song is signed by a library and they act as the publisher getting 100% of the publishers share. If I am the composer/writer, I get 100% of the publishers share. I assume that acting a publisher means that they are acting as the "Promoter" and since they procured a deal or placement they are getting the publishers share. What does that actually mean though. If Library A goes to a music supe and says here's a great song and they say cool we'll use it, is there a standard fee that is paid to the publisher? Does that also apply to the writers? What happens if I get a direct to supervisor forward and I get a call back. Would I be acting as the publisher and be entitled to the publishers share, or does the supervisor take that? If I am acting as the publisher, do I need to set up a publishing account with my PRO to make sure I am compensated for the publishing deals as well as the sync and writers?
I think that is where I find things confusing. Any info would be greatly appreciated. Cheers.