Transmission lines can transport electricity with less loss at higher voltages.
It is perhaps easiest to explain current and voltage by relating it to water flowing through a pipe. Current would be how much water is flowing, say by using a measurement like the number of cubic feet per minute. Voltage would be the pressure on the water. The power is delivered to major substations where the voltage is dropped to either 115,000 or 69,000 volts. From there the electricity is carried on utility transmission lines to our utility's substations where the voltage is decreased again.