In number 1, the center cell only has one
living neighbor, so it would turn white.
In number 2, the center cell has three living neighbors, and here we see it remains alive if
two or three neighbors are alive, so
it would be black at the next time step.
And on this one,
there's four neighbors,
so we get overcrowding
for the middle neighbor,
and not two or three, but
four neighbors are alive,
so this would be white at
the next time step.