With this worksheet, you can change the point A by using the slide bar a. This will give you the point (a, f(a)). You can also change the point B using slide bar b, this is the point (b, f(b)). Notice the secant line and the secant line equation (in purple).
You can click on the function, f(x) and when you get the text box change it to whatever you want. You are limited to the points between -10 and 10. some of the points MAY not show up on the screen.

As you look this over, make sure you understand that the average rate of change is JUST the slope between two points on a curve. The Secant line is the line that goes through those two points.