In Europe from the Middle Ages until the Industrial Revolution, a churn was usually as simple as a barrel with a plunger in it, moved by hand.
Today's commercial butter making is a product of the knowledge and experience gained over the years in such matters as hygiene, bacterial acidifying and heat treatment, as well as the rapid technical development that has led to the advanced machinery now used.
Butter is made from cream that has been separated from whole milk and then cooled; fat droplets clump more easily when hard rather than soft.
[1] With electric mixers and food processors commonly available in most household kitchens, people can make butter in their own homes without a large churn.
If the weather be cold put boiling water into the churn for half an hour before you want to use it; when that is poured off strain in the cream through a buttered cloth.
The butter is then to be placed on a board or marble slab and salted to taste; then with a cream cloth, wrung out in spring water, press all the moisture from it.