To learn the technical aspect of it, you can follow any network engineering certification materials or resources that delve into dynamic routing protocols, notably BGP. Inter-ISP networking is nothing but setting up BGP sessions and filters at the technical level. Why you set these up, and under what conditions is a whole different can of worms, though.
The business and political aspect is a bit more difficult to learn without practice, but a good simulacrum can be taking part in a project like dn42, or even just getting an ASN and some IPv6 PA space and trying to announce it somewhere. However, this is no substitute for actual experience running an ISP, negotiating percentile billing rates with salespeople, getting into IXes, answering peering requests, getting rejected from peering requests, etc. :)
Disclaimer: I helped start a non-profit ISP in part to learn about these things in practice.