Reparameterizing coordinates

I need a little a help, i just started learning grasshopper and i'm stuck with a problem. Its killing me. I'm learning from AAD Algorithms-Aided Design. Parametric St by: Arturo Tedeschi and there is this example: 

and this is how far i got:

I need some help with the part: "The bricks' gravity points (whose coordinates

were reparameterized between 0 and 1) were used as UV points for the Image Sampler."

I trying to solve it but for now is beyond my understanding of the program. A little help will really help me learn the basics.

And there is any other book you recommend reading? I really like this one but after i finish this one a want to learn more.

Thanks in advance.