what do windmills do

Windmills use the wind’s motion to do useful work. Traditionally, they were used to grind grain and pump water; modern windmills, usually called wind turbines, generate electricity.

What they do

• Turn wind energy into mechanical motion.
• Use that motion to run a machine, like a millstone or water pump.
• In newer designs, spin a generator to make electricity.

Simple example

When the wind pushes the blades, they spin a shaft. That rotating shaft can either grind grain into flour or power a generator for electricity.

In one sentence

A windmill is a machine that captures wind and turns it into useful power.

TL;DR: Windmills mainly grind grain, pump water, or generate electricity.