I read somewhere that this can be used for the reverse polarity protection in the circuit. BU ti am quite confused with its operation. Can somebody help me with this.

^{simulate this circuit – Schematic created using CircuitLab}

I read somewhere that this can be used for the reverse polarity protection in the circuit. But I am quite confused with its operation. Can somebody help me with this.

^{simulate this circuit – Schematic created using CircuitLab}