Okay, so take two points on the line on the graph, say they're (-2, 4) and (3, -2). The equation for working out the gradient is (y2 - y1)/(x2 - x1), and all that means, is you do the y value in the second coordinate (-2) minus the y value in the first coordinate (4), and divide it by the x value in the second coordinate (3) minus the x value in the first coordinate (-2). In this example, you would write it as (-2 - 4)/(3 - 2), and then you can simplify it -6/1, so your gradient for this example would be -6. I've tried to explain it as best I can but let me know if you're still confused :)
