Moo'kalvas, also known as cows, are useful because they give milk. However, they must first be tamed and well fed. The first Moo'kalva can be found when passing The Bridge location. The Cowshed is already in the camp, but it's slightly destroyed and needs to be restored.
You can make Cow Feed in the Windmill from Water and Sweet Potatoes. As soon as the feed is ready, it'll move to the Cowshed. Drag the feed to the Moo'kalva in the Cowshed, and you will get a bucket of milk.