I will be creating the requested graph, but have in mind that normally your teacher would like to see a table with points that belong to the line, which you are to plot and join.
Let me use a few examples that make the estimation of these points easy:
For x = 0 then the function y = 1/3 x - 6 gives y = 0 - 8 = -6
Then our first point is (0, -6)
Second point:
for x = 3 we get y = (1/3) (3) - 6 = 1 - 6 = -5
So this point is (3, -5)
Now with the two points we can draw a line on the plane.
Give me a few minutes to draw such line and add a graph to the answer.
Notice the blue line that crosses the y-axis at y = - 6 (the y-intercept), and raising with a slope of 1/3.