This is a small set of grayscale values to help with creating black-and-white art.
The idea behind the arrangement of them is that every color in the top row has two corresponding colors- one beneath it, and one to the left of it- which can be used to shade and tint that color, respectively.
To put that in simpler terms:
If you wanted to use the third color in the top row,
you would use the color to the left to tint it,
and the color beneath to shade it.
And so on for all of the other colors.
Of course, you can use any combination of values that feels right to you. This arrangement is just something that helps me personally, so feel free to experiment.