Milking cows in Coral Island is no longer difficult because you will learn how to do it here.
You will need to purchase the Milk pail. So make your way to the following location on the map to buy it. This is the same place from where you purchase your cows.
Unluckily, you can purchase only one, but sometimes you can purchase two Milk pails. It depends. You need to go to a specific house after a little walk, and you will get it from here.
Get in and move toward the corner. The interior of this house is like a shop. So buy two of them, and get back to your cows. Go near your cows, press left-click, and you will start milking.
Utilizing the milk, you can also make some cheese. Keep pressing left-click and keep milking. So, that is how you can milk cows in Coral Island.