What are animals (chicken, sheep, and cow) for?
The animals give produce which can help you earn additional income, chickens will given you eggs, sheep will give you wool and cows will give milk.
When you have an animal you will notice it will have a timer. The initial timer is the time until your animal is full grown and hence capable of producing eggs/wool/milk, the timers after this point is how long until the next produce is ready for you to collect.
You will need to feed your animals regularly to keep them growing/producing. If you feed them fully, the food should last for 22 hours until you need to feed them again. Chickens eat Chicken Wheat, and Sheep and Cows eat Grass.
Chicken Wheat and Grass are crops that if you just grow to sell, you will not make profit from, so you should grow them primarily to feed your animals!