how does a zener diode work as a voltage regulator. Explain everything also define what actually is a zener diode along with all circuit diagrams

In contrast to a regular diode, a zener is designed to operate reverse biased in the breakover region. In that region, large changes in current through the diode result in minimial changes in voltage across the diode. If the diode is then placed in parallel with the "load", the two voltages will be equal. This results in very small voltage changes even when the current changes dramatically, hence voltage regulation.