We have a 6 x 6 image. On its left half we have all tens and on the right half, all zeros. If you plot this as an image, it might look like the one below it, where the left half shows brighter pixels and the right half depict darker pixels. We use a shade of gray to denote zeros. In this image, there is clearly a very strong vertical edge as it transitions from white to black or white to darker color. When you convolve this with the 3 by 3 filter, in the middle, with brighter pixels on the left, mid tone zeroes in the middle, and darker on the right, you'd get the matrix on the right. If we plot the right matrix's image, we will find a lighter region in the middle that corresponds to a vertical edge.