In short the Proto-Flow is our tool to visualize the steps the user will see/take in the prototype. It’s just not as detailed as a storyboard — as described in the book — it is more like a user flow diagramm. But it can still contain sketches of steps, if they are already clear on Wednesday. It usually also featues parts (post-it notes) of the solution storyboards to make the flow more understandable for the sprint team.

Hope this helps to understand the Proto-Flow better.

Have a great end of the year and enjoy 2018, Oliver