y = -5

Since the variable x does not appear in the equation,
x can be any number we choose.  However the value of
y can only be -5.

So to make a table of values of points, we don't need
to do any calculations, but just pick some arbitrary
values for the x-coordinate, the variable that does not 
appear in the equation, and use -5 for the y-coordinate:

  x  |  y  |  (x,y)
 -7  | -5  | (-7,-5)
 -4  | -5  | (-4,-5)
  1  | -5  |  (1,-5)
  5  | -5  |  (5,-5)
  8  | -5  |  (8,-5)

So we plot those 5 points:



Now we just draw a line through all those points (I'll draw it
in green):



So as you see, it's horizontal, not vertical.

Edwin