For the graph of y = -8 the line is horizontal, which means the slope = 0. A parallel line has the same slope so one equation could be y = 2. A perpendicular line has an opposite slope so since our slope = 0 the opposite of that slope is 
which a line that is perpendicular to y = -8 could be x = -3. Also notice that these two lines form a 90 degree angle.