Help in understanding Color-Based Segmentation Using the L*a*b* Color Space Example

Hi I am working on the picture I have attached below. I want to extract the boxes out of the picture by using Color Segmentation, for that I am following the example http://www.mathworks.com/examples/image/2087-color-based-segmentation-using-the-l-a-b-color-space

But I have problem in understanding following things.

1. what are " regioncoordinates"
2. What happens in the step 17. lab_fabric = RGB2Lab(fabric);
3. My picture doesn't have pure red,green and blue components, How can I modify this example for my boxes.