That takes an image called leleccum and stacks all columns on top of each other with col 1 at the top, then col 2 underneath that, then col 3 and so on. Then it extracts the first 3920 elements of that column vector into a new column vector. This may or may not be an exact integer number of columns.
To do it for an image of any other name, simple use the name of the other image.
For example to get the first 58 pixels in image "grayImage", do this: