This is a reasonable introduction.
https://www.ibm.com/z/resources/zxplore
There's also a bunch of (sign-in required) free training at learn.ibm.com. And I think there's something on Coursera too.
Re:Z/OS Introduction
by santoshalper on Friday February 17, 2023 @09:18AM
(#34834899)
It's definitely not a very large audience, and it is mostly people who either have to maintain a legacy system or want to integrate with one. The price/compute ratio on Z Series is terrible, but it is still highly effective for some workloads. Really though, anyone doing development on a Z Series today is almost certainly just maintaining a legacy core system.
I don't think that would be a very large audience, but I wonder how people actually do learn about ZSeries. I know there is an official Developer Thing Z/pDT or some such, that I gather is a mainframe emulator.