In this simulation you can adjust the charge and position of the two charges using the sliders or the input boxes. The sliders work, but do not work smoothly due to the complexity of the calculations - so you may be better off using the input boxes. Choose to view in 3D and the Electric Potential is shown as the third dimension. Choose the equipotential view and you'll see a 2D view with equipotential lines. In this view you can also choose to see vectors showing the direction of the electric field. In the equipotential view, there is also a movable point that shows the magnitude and direction of the electric field as well as the electric potential at that point.