In a linear function, the formula you are looking at is in point-slope form. y=mx+b
m is the slope. In this case, the slope is 2. slope is rise over run. 2 in fraction form is 2 over 1, meaning for every 1 unit you move on the x-axis, you'll move 2 units on the y-axis.
b is the y-intercept. The y-intercept is the point on the y-axis of the graph. Since the y-intercept is -1, you know one of the points is (0, -1). Place that point on your graph, then use the slope from earlier (rise 2, run 1) to add more points to the graph.
