First select a reaction from the list on the upper right. For the experiments suggested in your Student Guidebook, you should use the 1A + 1B <=> 1C reaction. Next, set up a reaction by typing a value for DG° into the indicated box and setting the initial amounts of reactants and products. Set the amount of each species by either typing in the appropriate box, clicking-and-dragging on the top of the colored bar, or clicking on the + or - buttons. Input amounts can range from 0.0 to 10.0 moles. Click on the REACT button and observe the changes.
You should carefully observe what happens to the DG° gauge and the DG gauge in the middle of the right panel. Also notice how the amount of reactants and products changes from beginning to end of the reaction.