The Itinera book
Itinera is a workflow framework that keeps business rules separate from flow control. This book shows you how to build with it, one small online shop at a time.
It is one book, written for several programming languages. Pick the language you build with, and read the whole book in it: every example is a complete program that compiles and runs, and what it prints is shown underneath.
Separating process from logic was good practice before coding agents; now it makes their work safer, because a change to a step cannot take a flow decision, and every flow decision is declared in one workflow. Why Itinera, on the Itinera site, tells that story.