The most direct form to graph a line, is to find two points of it and connect them with a line.
Here we have:

Let's find the point where x = 0. To do this, we replace the x in the equation by 0:

We have our first point: (0, -6)
Next let's find the point where y = 0. Again, we replace y in by 0 in the equation:

We have our second point, (3, 0)
Now all we have to do is plot the points (0, -6) and (3, 0) in the plane, and connect them with a line, and then the line is graphed
The line should look like this: