Milk comes out of the cow as "Whole Milk" as is, with nothing added or removed. This is NOT what you are drinking, unless you are a farmer, you are drinking "Whole Standardized Milk" which means it has gone through many different processes to make it safer to drink and to have a longer shelf life. The two most important processes are "Pasteurization" and "Homogenization."
Pasteurization is the process of heating the milk to a temperature of no less than 71.7ºC for a minimum of 15 seconds (max 25 seconds) so most germs are killed.
Homogenization of milk involves forcing the milk at high pressure through small holes. This breaks up the fat so it spreads evenly throughout the milk and prevents separation of a cream layer when it sits. "Whole Standardized Milk" is where all dairy begins and is derived from.
This kind of leads us to cream, heavy cream, heavy whipping cream, or whatever else you want to call it are all the same thing. It is the fat rich part of the milk. The cream rises to the top when milk is fresh and is skimmed off to harvest it. This is how we have different levels of fat or "Butterfat Content" in our milk. The "Butterfat" is removed from the "Whole Standardized Milk" then the correct amount is returned to produce whatever type of milk you like.
Some of them are as follows:
1% and 2%- Obviously, 1% or 2% butterfat is added back to the fat-less milk each accordingly.
Skim-Also known as "Nonfat" milk, food with less than 1/2 a gram of fat per serving can be labelled "fat free"
Heavy Cream- Butterfat content between 36 and 40%. Being high in fat is the reason you can make whip cream out of it, the high level of fat stabilizes it and holds it together.
Butter- 80% Butterfat, the other 20% is milk solids and water. Made by churning cream until it separates into butter and buttermilk.
"Traditional Buttermilk"- Was the leftover milk from churning cream or milk into butter. (Now buttermilk is made by a culture from a natural bacteria for mass production)Evaporated Milk- Is evaporated under high pressure to create a concentrated milk product, it is also sterilized.
Condensed Milk- is concentrated in the same way as evaporated milk, but with the addition of sugar.
(This product is not sterilized but is preserved by the high concentration of sugar.)
There is a lot more dairy to cover but this is the most of it as far as cows milk is concerned. Hope this didn't spoil (milk pun) anything for you.