This is known as the BGP book: https://www.amazon.com/Internet-Routing-Architectures-2nd-Ha...

It goes into detail. If you're just starting out, get a Network+, Security+ or any other systems administration, security or networking certification that covers the basics of networking and internetworking.

Well that was not what I expected. (Especially the “there’s really nothing difficult” part.)

If you really want to understand BGP, read https://www.amazon.com/Internet-Routing-Architectures-2nd-Ha...

or, if you’re looking for something online: http://www.tcpipguide.com/free/t_TCPIPBorderGatewayProtocolB...