How does a flourmill work?​

In a commercial mill, the grain is cleaned then “tempered", which means the grain is soaked in water to enlarge its moisture content to make it easier to roll. After it's tempered, the grain is moved through a series of rollers, which break up the grain into its separate parts: endosperm, bran and germ.

What is the use of flour mill?
A gristmill (also: grist mill, corn mill, flour mill, feed mill or feedmill) grinds cereal grain into flour and middlings. The term can refer to either the grinding mechanism or the building that holds it. Grist is grain that has been separated from its chaff in preparation for grinding.