I just learned this. Rise over run is also rise divided by run. The rise refers to the y axis (since y is vertical so it's rising), and run refers to the x axis (Since x is horizontal so it's running straight). So in other words, rise/run = y/x. To calculate the slope, you do y/x. For example, if you have y=3 and x=8, then your slope is 3/8. To plot that on a graph, you start from your point, and go up three, and across 8. Hope this helps.