Butter is made by taking the cream from the milk, then churning this (effectively shaking it). Butter can be made from fresh or sour cream and often has a little salt added to lengthen its shelf life. Butter has a fat content of around 80%. Both salted and unsalted versions are generally available.
Butter is used as a spread on bread or toast, or as an oil for light frying or sautéing. Butter can also be softened and then flavoured with herbs, especially garlic for garlic butter or garlic bread, or other flavours like mustard or anchovies.
Dowell, P., Bailey, A. (1980) The Book of Ingredients, Dorling Kindersley. ISBN 0718119150.