You plug in numbers -3 to 3 into the x variable of the equation and then plot those points
y = -2x
X = -3 y = (-2)(-3) = 6
X = -2 y = (-2)(-2) = 4
X = -1 y = (-2)(-1) = 2
X = 0 y = (-2)(0) = 0
X = 1 y = (-2)(1) = -2
X = 2 y =(-2)(2) = -4
X = 3 y = (-2)(3) = -6
In case that looks a little cluttered here are the points to graph:
(-3, 6) (-2, 4) (-1, 2) (0, 0) (1, -2) (2, -4) (3, -6)