The document is arranged in parts with chapters 1 and 2 as an introduction for everyone who performs z/OS migration actions regardless of the migration path and migration paths for hardware, chapter 3 for those customers migrating from z/OS V1R13, and chapter 4 for those customers migrating from z/OS V1R12. For chapters 3 and 4 only those actions for the specific migration path are documented. See How this document is organized.
This document does not explain how to exploit new functions in z/OS. For that information, see the many publications that pertain to the z/OS base elements and optional features.