Household electricity uses only “one” hot wire. The other carries no current at all until it completes a circuit.
Actually, at the transformer, the center tap of the secondary coil goes to the earth. The voltage between the outer taps is 240 volts. The voltage between each of the outer taps and the center tap is 120 volts. The earth acts as a giant capacitor or reservoir. If you touch the grounded or neutral wire you won’t experience any shock because you are at the same potential as the earth. If you touch the ungrounded or hot wire, you will receive a shock–the severity depends upon the resistance between you and the earth.
With an automobile, the connection of the battery terminal isn’t made to the earth, but to the chassis of the car.