Initially you see the "Bounds and Frame" menu. Here you can set the names of the X and Y axis variables and the X and Y axis scales, and then label the axes by clicking "Draw Frame". Then change to the "Function plotter" menu (click on "Bounds and Frame" and choose "Function Plotter"). Enter the function in the box after "y =". It should be an expression involving the variable you chose to label the X axis in "Bounds and Frame" (the default is x). Then the "Plot function" and "Plot derivative" buttons plot this function and its derivative respectively. Note that any variables other than this one will be taken to be 0. "Step size" is the interval between values of the X axis variable at which the function is calculated, and "colour" controls the colour of the curve. You might want to change this between pressing "Plot function" and "Plot derivative".