What is the difference between a Zener diode and a normal diode? What is the use?

The difference is in the role and the principle of action.

The Zener diode uses the reverse-phase breakdown of the P-N junction of the diode to stabilize the voltage, and the breakdown voltage of the P-N junction thickness is high.

The common tube is characterized by the use of a diode to conduct a reverse-phase non-conducting energy, mainly for isolation and rectification.

The Zener diode is mainly used as a voltage regulator or voltage reference component. Zener diodes can be connected in series for use at higher voltages, resulting in higher regulated voltages in series.