Animals produce valuable products that will help you improve your production. To buy an animal, set up a farm for it first. It can be bought in the market. Drag the building to the cleaned location, then buy an animal and place it near the farm.
Feed the animal in order to start production. By tapping on the animal farm, you can see what kind of food is needed for this animal, as well as where to get it, if you tap on the magnifying glass.