I'm sorry that you are frustrated. We can't provide tutorials for all possible implementations. The documentation you are reading is talking about a concept you can use in general to update rules to fit your needs. However it isn't a complete example of how to integrate those with paypal.
I'll try to help with more direct instructions instead of explaining concepts. Maybe that will work.
I think your easiest solution is to not update the TotalPrice calculation.
Instead add a rule to the Shipping section that sets a shipping rule equal to the total of the ShippingTotal calculation you have added.