Hard hats protect you by providing the following features:

A rigid shell that resists and deflects blows to the head.

A suspension system inside the hat that acts as a shock absorber.

Some hats serve as an insulator against electrical shocks.

Shields your scalp, face, neck, and shoulders against splashes, spills, and drips.
Some hard hats can be modified so you can add face shields, goggles, hoods, or hearing protection to them.