Hello Everyone

I have a question about having a payment split. For example we have user A user B and user C. User C creates website to help user A and B conduct transactions. User A pays user B. How can user C receive a small percentage of the transaction? I'm not looking for the exact answer to this question because I know this is not a short sweet answer however I am asking if anyone knows any resources. I've been trying to find this for a while with no luck. Can anyone point me to the right direction so I may research how splitting a payment works? Can't figure out how this works. Is it 2 transactions or should it be set up that user C receives all payment and then sends user B his amount. Thank you.