When you left-click to place the test charge, it will immediately begin to move under the influence of the local electric field. If you want to slow the action down to see things happen more clearly, use the View Speed slider bar in the "Controls" panel.

As a test charge moves, its speed, kinetic energy, and electric potential energy are shown in a box in the upper-left corner of the grid area. Watch the values as the test charge moves. How does the total energy (kinetic plus electric potential energy) behave?

You may place more than one test charge on the grid at once (10 at most). If you do, the statistics of the most recently created test charge are shown in the box.