In order for the electrical power distribution network to function, voltages must be stepped up before power is transmitted great distances over power lines. One major problem is that power is lost between the power plant and the consumers because currents use some of the power to heat the transmission lines. The power transmitted along the line is equal to the voltage times the current. The higher the voltage the lower the current that must flow within the transmission lines to deliver the same power.
Lower currents produce much less heating and much less power loss.
Transformers are the critical elements that step up and down the voltages at each end of the line. A transformer is just a piece of iron with a pair of wires coiled around it - one with many more turns in the coil than the other. The coils of wire are not physically connected. The iron core is immersed in an insulating oil bath which does not conduct electricity well. The basic physical process underlying the operation of transformers is electromagnetic induction.