The Slope-Intercept form of the equation of a line is: y=mx + b
where m=slope (often called "rise over run")
b = y-intercept (the point on the y-axis when x=0)
Given a slope and a y-intercept point [ (0,b) ],
(1) plot the point (0,b)
On the y-axis (x=0), find the point b.
(2) Now, do the "rise over run" exercise. For a slope of m, you go up m units on the y-axis for 1 unit of increase on the x-axis. For example, if m=4 the next point after (0,b) would be (1,b+4). Now, note that a negative m (a negative slope) means that the y-values decrease as the x-values increase.
Two points determine a line. "Connect the dots" and extend in both directions.