Buy hay from Marnie or grow grass and cut it with a scythe
Make sure you have a silo so cut grass is stored as hay
Open the coop door if you want chickens to eat outside grass during the day
Go inside the coop and place hay on the feeding bench from the hopper
Use the hay hopper inside the coop to automatically dispense hay
Keep the coop upgraded so it can support more chickens
Check the feeding bench every day to confirm there is enough hay
Feed chickens daily in winter or rainy days when they stay inside
Let chickens eat grass outdoors when the weather is good and the coop door is open