If you have a point on a line, you continue the line based on the slope. For example, if you know that point (1,2) was a point on a given line, and that 1/4 was it's slope, the next point would be (5,3), which is found by adding the run (denominator of the slope; in this case, 4) to the x-coordinate of the given point, and adding the rise (numerator; in this case, 1) to the y-coordinate.