[O.B.Left]

I'm having a hard time understanding the hinge action.

You , me and almost everybody else.

Lynn once said something to the effect of "its takes about 5 years to fully understand hinge action". You could argue that even some of TGMs greats didnt get it totally correct either.

If you have the book look up the drawings in chapter 2 and see how Horizontal is the ideal for ball compression , distance. Combine that with a good club head path and your game will take off.

Something to consider is that its not done with the hands as you mentioned. It seems like that at first, but it isn't so. Properly executed , Horizontal will not cause a hook.