What happens during the regulation action of a Zener diode?

In the following circuit,the current flowing through the Zener diode is (in $\text{ mA}$)

If the current in the Zener diode is five times the current in $R_1$ and the breakdown voltage of the diode is $6 \text{ V}$,find the value of $R$.

Manufacturers supply a zener diode with zener voltage $V_{z}=5.6 \, V$ and maximum power dissipation $P_{z \max }=\frac{1}{4} \, W$. This zener diode is used in the following circuit. Calculate the minimum value of the resistance $R_s$ in the circuit so that the zener diode will not burn when the input voltage is $V_{in}=10 \, V$. (in $\Omega$)

Mention the use of a Zener diode.

$A$ reverse biased Zener diode when operated in the breakdown region works as