This is a reasonable introduction. https://www.ibm.com/z/resources/zxplore https://www.ibm.com/z/resources/zxplore There's also a bunch of (sign-in required)

This is a reasonable introduction. https://www.ibm.com/z/resources/zxplore 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.