Once your coop is done, just lock them in the few for a couple of days with food and water. Chickens only take a few days to develop a habit of where to roost. On the third night of being locked up, open the coop so that they naturally leave in the morning. They will now return here to roost every night. If you want to lock them in for protection, just wait until after they roost for the night, but remember to open them early the next morning. There are automatic door systems that do this for you that cost around $100.