Things are challenge

To learn the computer science, the logic thinking is the most important thing we should care about. Once you have a clear logic, you could understand the codes much easier. I believe my logic thinking is not bad. I can understand most of the code very fast, but there are still some thing really confuse me. The first thing is the code "map-image" I could not understand how they use this code to achieve "number-->image" and another one I know how to use but could not understand well is "list-color". I am confusing how they connect the number to the color that well.