You can drag more charges and observers out from the two square boxes at the top right hand corner. Drag them back to remove.
To add equipotential, first select an observer then click the "Add equipotential" button.
Tip: Try not to show both field lines and equipotentials at the same time otherwise it may look too messy. You can control this by using the show/hide buttons.
Can you see the electric field always points perpendicular to the equipotentials?
