Liquid fats, in the form of milk, are excreted from mammary glands in the cow's udder. The udder is along the cow's stomach, just in front of the two hind legs. The udder is analogous to human breasts in the fact that it is made up from mammary glands and the milk is expelled through nipples. However, on the cow, there are four nipples on the one udder, as opposed to one nipple per breast on a human.
Milk is produced by cows for the same reason all mammals produce milk- to feed their young. In agricultural contexts, a cow's milk may also be consumed by humans or made into products like butter (primarily made of the milk fats) or yoghurt.
Milk fat is primarily saturated fat, though there are also monounsaturated and polyunsaturated fats in milk. Fats make up about 3.4% of the liquid milk, though this level of fat may be altered for human consumption, as with skimmed milk.