How does the payment card system work?

I don't know if this is the right sub for this question, but if it isn't I don't know what is.

If someone could answer a few key things that would be greatly appreciated.

What protocols do credit/debit card transactions use(i.e. I use my card at McDonalds, how is cost info sent to my bank)?

What does a transaction look like on a network? Packet layout, data structure, that sort of thing.

Is any part of this system open source/ have public information available?

I've googled this many times and all of the articles I've found just explain how banks work on a broad scale and don't discuss the means by which it actually happens.

Thanks in advance.