In this simulation, you can investigate the electric field at various positions along a line, when there are either one or two charged particles on that line.
The electric field is represented in two ways. First, there is a movable positive test charge that you can move along the line to sample the field at various locations - the direction of the force on that test charge is the same as the direction of the electric force on the test charge.
The second way to represent the electric field is to plot a graph of the electric field as a function of position. For the graph, we define positive field as a field pointing to the right, and negative field as a field pointing to the left.