How voltage regulator on motherboard work?

Answer 1

There are several.

Some use an A/C inverter. The DC is put through an oscillator using a coil. A switching transistor then charges a capacitor, while a dedicated power supply chip controls the mark/space ratio of the pulses, to regulate the voltage and current.

Simpler devices, like the 7805, are power transistors which have a zener base reference, to control the voltage passed by the transistor. These just add resistance to a higher voltage and reduce it to a lower one. They run quite hot and have heat sinks.

Answer 2

A mechanical voltage regulator works by using resistance and heat to adjust and regulate voltage. As certain conductors of electricity change the conductive properties when a change in temperature, this changes are used to regulate and adjust voltage.

Answer 3

A Voltage Regulator is just a Zener Diode that is wired across the alternator terminals.

... no.

Doing this will blow the zener - don't try it at home or anywhere else.