This guide will let you know what a Coffee Grinder is and how to use it in Guardian Tales. Go through the guide and follow the steps to use it.
You will find a coffee grinder resource when you are in the shop, as shown in the image below.
You have to buy a coffee grinder, and you will need 5 coffee grinders before it takes effect. Once you have five of them, it will increase your max stamina by 1 point and recharger your stamina by the amount of your total stamina.