Step 1: Raw Milk
Pasteurizing= We DO cook milk! In simplest terms the milk collected from dairies is super-heated then rapidly cooled. This process kills most bacteria & microbes. It also destroys some of the nutritional value & flavor of the milk, but it does however make it safer to drink & reduces spoilage.
Homogenizing= This process essentially prevents the cream from separating by pushing the milk through a series of screens or tubes at high pressures. This causes the large fat globules in the milk to be broken into much smaller globules creating more consistent emulsion, therefore no/ little separation.
As far as butter making goes, you will get a more flavorful product using the cream from raw milk, however it will spoil faster & has more potential pathogens in it. It is also faster to make the butter because the fat globules are still relatively large so half the work is done for you. We always used the cream from raw milk because it was available to us. My mother would literally walk into the barn & scoop some cream from the bulk. Since raw milk isn't easily accessed now a days, I've done this instructable using store bought heavy whipping cream.