How does the net charge relate to electromagnetic fields?
Charges are the basic source of electromagnetic fields.
An oscillating charge produces EM Waves of it's own frequency. We are familiar with the fact that a static electric charge produces a steady electric field around it given by,
Now, if it oscillates (or anyways accelerates), the electric field changes with time in the space. This generates a magnetic field from which can be understood with arguments from the familiar Maxwell's correction in Ampere's circuital theorem.
The time varying electromagnetic fields thus, regenerate each other and propagate through space.