To cook in Zelda, BOTW, open your inventory, select the food item you wish to cook and choose ‘hold’. You can hold up to five items of food. Held food can then be put into a cooking pot (the preferred method of cooking, as it unleashes special effects, which is essential if you want stamina boosts, etc) or simply tossed into a fire to toast or roast. Throwing food into a fire will work if all you want to do is get some health back, but it’s a waste if you want the special cooked effects.
Zelda rewards experimentation, so don’t be afraid to pick up different ingredients and toss them into your cooking pot all together, even if they don’t seem like a natural match. Also, don’t be afraid to experiment with various edible items. You can eat anything from acorns to caterpillars.
Where to find cooking pots? Cooking pots can be found at many camp sites (usually infested with Bokoblins) and various other places. The old man on the Grand Plateau keeps several spots open with fires and cooking pots, and often stacks other useful items nearby.
Learning what foods stack which effects is the most important part of cooking.
This eurogamer article has a comprehensive list of all Zelda foods and effects, in handy chart form, just like the game didn’t provide!