So an array width 4
x indexes are
0 | 1 | 2 | 3
array.width-1 = 3, which would be the last column. Since I pushed to the back of the array.
If you push to the front of the array, you would simply use 0. I don't remember if I had a particular reason to push to the back...
As for what it does - After pushing current pick to the back, it only sets the first row value (y0). So I need to move the other values in the other two rows (y1 and y2) as well..