At the top of the applet on the left you will see the bar. To set the bar in motion, click on it and drag around to deform it, or click "Fundamental".
Below the bar you will see a graph showing each normal mode's contribution to the bar's vibration. There are two sets of indicators; on top are the magnitude indicators, which shows the amplitude of each normal mode. These can be adjusted with the mouse, or you could double-click on one to isolate a particular mode.
The setup menu in the upper right has other variants of the bar (with different boundary conditions) for you to try.