Recall the concept f '(a) is the slope of f(x) at x = a:
a) if f(x) is increasing, f '(x) > 0, which means the graph of y = f '(x) falls above the x-axis;
b) if f(x) is constant or reach to an extremum, f '(x) = 0, which means the graph of y = f '(x) falls on the x-axis;
c) if f(x) is decreasing, f '(x) < 0, which means the graph of y = f '(x) falls below the x-axis.
If you wish try out your understanding towards the concept above, perhaps you can ask your friend's help to give you a graph of a function (remember, a function is a one-to-one or many-to-one relationship) and you may try to sketch its derivative graph.
Betty, Created with GeoGebra