To use this skill you need access to a fire (campfire, oven or even a forge). Double-click on a food item, then on the fire to try to cook it. Cooking skill also lets you try to combine certain objects to make baked goods.
Use water on flour to make dough.
Use dough with fruit, meat or vegetables to make a pie.
Use dough with honey to make sweet dough.
Use sweet dough and flour to make cake mix.
Use sweet dough and more honey to make cookie mix.
If you use a bladed object on a caught fish, the Cooking skill will also allow you to bone and gut it into raw fish steaks.