Windmill

A Windmill is a building where you take grain, and turn it into flour. You can then use an empty pot on the flour from the chute at the bottom, and keep it for various uses with the Cooking skill. In the Cook's Assistant quest, the Cook asks you to get flour. There are a few Windmills throughout :
 * North of Lumbridge
 * North of East Ardougne
 * In the Cooking Guild west of Varrock
 * Zanaris

Flour mills are generally three-story buildings with decorative millstones in the middle. The mill in Zanaris is special in that it's only one-story and has no millstones to be seen. It is southwest of a nearby wheat field and fountain. With a bank to the northwest, it's the best place to prepare items in large quantities that require flour.

Step to make flour

 * 1) Pick grain from a wheat field
 * 2) Go to the top of the mill and use the grain with hopper
 * 3) Operate the hopper
 * 4) Go back down to the ground floor and use an empty pot with the flour in the chute

The flour in the chute works like a dropped item. After a period of time, it will be visible for everyone to grab.