Numerous item descriptions have made reference to cooking, and there's a cooked segment of the inventory. I'm not sure how to cook, though - there doesn't seem to be a clear prompt.
How can I cook my food?
According to this site, you have to:
Approach a metal bowl. Light a fire underneath it if necessary. Press + to enter your inventory screen, and choose up to five ingredients to hold. Approach the bowl and, when prompted, press A to cook. It’s that simple.
Additional information is found on the site in question, including cooking elixirs and what types of foods you can cook.
There are several methods to prepare your ingredients:
Another method of cooking is by using a Fire or a hot location, such as Death Mountain. Simply drop the item you wish to cook near the fire or on Death Mountain, and it will cook after a short time.