In the world, generation, distribution, transmission was carried out with continuous energy, as time went by, engineering evolved with the incursion of alternative energy.
Historically, electrical energy is generated by means of electrolyte. The electrolyte, a chemical that reacts with the electrodes, in such a way that one of them gets the electrons released by the reaction becoming negative, while the other, having lost them, acquires a positive charge. This difference in charges between the two electrodes is the "potential difference".
If an external conductive cable that communicates them is connected, the difference in potential causes a path through which the electrons of the negative electrode pass to the positive electrode. Precisely, the displacement of electrons through a conductor is known as "electric current".
Another way to get continuous energy is by using dynamos (rotating electric machine that generates alternating energy in principle, but with the use of brushes and sliding rings it is converted into continuous energy).
Currently, the continuous energy is obtained by applying the electronics through devices called rectifiers.