Emma milks her cow, Rosie, in a special stall in the barn that has a milking stanchion. A milking stanchion is a frame structure which holds a cow in one place while a person is milking it. If a cow is not put in a milking stanchion, she may try to leave or move around during the milking process, which would make milking her very difficult.
The stanchion will usually have a feed trough with a set of bars or slats in front of the trough. When the cow comes into the stanchion to be milked, she will put her head through the bars to get to the food in her trough. A person can then slide the bars closer together and lock them in place so that the cow can no longer pull her head through. The cow can still move her head up and down, though, and is able to eat out of the feed trough while she is being milked. When the milking is finished, the bars will be slid apart again so that the cow can back out of the stanchion.
Emma only has one milk cow, so she milks Rosie by hand. A large dairy farm with many milk cows will have many milking stanchions side by side so that a large number of cows can be milked at the same time. A dairy farm will also use milking machines so that the milking can be done more quickly and easily.