Cows are a passive mob found mostly in grassy biomes and they are a great source of resources such as beef, milk, and leather. They were added to Minecraft in alpha patch 1.0.8 of the Java Edition, they weren't in the game at the initial release and like many others were added as the game has evolved and grown.
A cow in a grass plain (Via Screenshots)
Cows usually spawn in grassy biomes in small herds during world generation. Their spawn rates vary from one biome to another. For Bedrock Edition players cows spawn on grass blocks with a light level of 9 or higher, whereas for Java Edition players cows required only a light level of 7 at the lowest to spawn. In both editions, they don't spawn in snowy taigas, snowy plains, meadows, mangrove swamps, and the wooded badlands.
Sometimes they can spawn inside animal pens and butchers’ houses in villages. On rare occasions (5% chance) they can spawn as a calf. They also have a very rare variant known as Mooshrooms or mushroom cows which spawn in the mushroom biomes.
Cows in their natural habitat (Via Screenshots)
Cows like to roam around in herds aimlessly and tend to walk around mooing. They don't interact with the player much, they will just stare at you for a couple of seconds and then go back to grass-munching business as usual. If you wish to lead/bring them to your house, you can use a lead or equip some wheat in your hand.
When the cows see the wheat they will start following you as long as you keep it in your hand and do not go farther than 6 blocks from the cow. Sometimes they can be seen jumping up small inclines and even falling to their deaths from cliffs. They are not afraid of water and can be spotted sometimes in a water body bobbing up and down to stay afloat. Like most passive mobs they flee when attacked. When fleeing they are 25% faster for a few seconds.
Cows following a player with wheat in their hands (Via Screenshots)
Cows are a very useful and important mob for players as they provide the player with raw beef, milk, and leather. To obtain raw beef and leather from cows they must be killed, whereas to get milk the player needs to right-click them with an empty bucket in hand. All of their products are easy to get if you have a wheat farm in operation.
One of the most common uses is to get 2 cows into an animal pen and breed them to have a constant supply of raw beef so keep yourself fed.
Cows in a pen for breeding (Via Screenshots)
When killed cows drop 2-3 pieces of raw beef along with 0-2 pieces of leather. The drop rate of leather is around 25%. Milk isn’t a drop but can be obtained with the help of an empty bucket.
If killed by a player or a tamed wolf 1-3 experience points are dropped, breeding them can drop between 1-7 experience points.
When killed with fire they drop cooked beef instead of raw. You can also get mushrooms from the mooshroom variant of the cow by shearing it, it will drop 5 mushrooms corresponding to the type of mooshroom, and doing so leads to the mooshroom turning into a regular cow. Mooshrooms also give mushroom stews when milked.
Items you can get from cows (Via Screenshots)
To breed cows you need to feed two of them a portion of wheat. Many red hearts appear around both of the cows when they are fed. Calves are the result of cow breeding. Like other baby animals, they do not drop anything when killed but like their adult counterparts, they can be milked despite their immaturity.
A calf takes one Minecraft day (20 minutes) to mature but it can be reduced by feeding the calf wheat, each time it is fed wheat it reduces the time taken for growth by 10%. Calves usually stay close to their parents, in cases where the calf is separated from its parents by 24 or more blocks, it will look for another adult cow. There is no limit to the number of times a cow can be bred but there is a cooldown of 5 minutes before you can breed them again.
A player breeds cows (Via Screenshots)
Cows were first added all the way back in the Alpha of Java Edition v1.0.8 to be precise. Back then cows were black and white and made strange sounds. But by v1.0.14 their color was changed to brown with white spots and a 3D udder was added. Minor changes are done to the Cow model during the prerelease stage with its horn moved around a couple of times and some changes to textures along with some updates to their AI.
One of the major updates was the addition of Calves during this stage. The next major update was to change where they could spawn, some biomes such as the snowy taigas were removed and places like villages and animal pens were added and growth acceleration for calves was also introduced.
So cows have been a very helpful and important mob in Minecraft, from providing food to basic armor components they are a very useful mob, especially at the beginning of your adventure. Mojang has done an amazing job at updating and making welcome changes in order to make the cows more useful and not just walking food. Now equipped with all there is to know about them, make sure to yield all the benefits cows have to offer.
A. Baby cows need to eat 3-4 blocks of grass in order to grow up, Adults don't need to eat grass.
A. You need a portion of wheat equipped in your hands, and be closer than 6 blocks to the cow to make it follow you.
A. No, you cannot turn a cow into a mooshroom.