In my textbook it says:
One of the rules for static electric fields and conductors is that the electric field must be perpendicular to the surface of any conductor. This implies that a conductor is an equipotential surface in static situations. There can be no voltage difference across the surface of a conductor, or charges will flow. One of the uses of this fact is that a conductor can be fixed at zero volts by connecting it to the earth with a good conductor—a process called grounding. Grounding can be a useful safety tool. For example, grounding the metal case of an electrical appliance ensures that it is at zero volts relative to the earth.
I understand that there is no movement of charge in conductors in electrostatic conditions, and hence there must be no voltage across the conductor is 0. However, how would connecting it to ground fix it as 0 volts. Is it because if any extra charge enters the conductor it will immediately will go the earth? Secondly, why does it have the connection to the earth have to be with an equipotential surface?