Slope is (change in y)/(change in x). If you have a slope of -2/3 the change in y is -2 and the change in x is 3. Find the point (-2, 1) on the xy plane. Change the y component by -2 (move down 2 grid lines) then change the x component by 3 (move to the right 3 grid lines). If you repeat this process in both directions then draw a line through the points you'll have a line with slope -2/3 which passes through the point (-2, 1). The equation of this line is: y=-2/3x-1/3