Since charges are free to move in a conductor, when an external electric field is applied to a conductor, they will rearrange themselves in a conductor until any external field is exactly canceled out by the rearranged charge distribution. This means that the electric field inside a conductor is always zero and any conducting shell will act as a perfect shield against external electric fields. Electrical storms can create huge electric fields and produce huge electrical discharges in the form of lightning, however, if you remain inside a metallic car you are shielded from the effects of the electrical storm. The most common form of an electric current is the flow of electrons in a conductor. Currents occur in all materials, but the amount of current depends on the nature of the material.
All materials belong to one of four basic categories.
The easiest method of producing a current is to apply an external electric field to a conducting material. This causes the free electrons to move inside the conducting material in response to the applied electric field. This is very much like the plumbing system in a house. In such a system there are two sets of pipes, one carrying the fresh water to wherever it is needed and a drainage system to carry the water away after it has been used. The other two are connected to the electrical network of the power company.