Cooking can be done on most of the various fire sources in Survival Plus. Everything except meat must be cooked in a container. At the primitive level this would be the clay Food Storage Pot created in the Pottery Wheel. As you advance you will get access to a Metal Pot made from common ingots, and beyond that you will be able to make or purchase items from the Mason and Blacksmith for advanced cooking.
You will find all the meals you are capable of cooking in the menu of the fire itself. Once you have added all the required ingredients to the burning fire, along with the container you are using to cook with, the items will be consumed and after a short delay, the food item will appear.
The nutritional value of cooked meals will always exceed that of raw food items, and for the advanced Farmer meals, far more.
You can find more information about meals here: Meals
You will find information about nutrition here: Nutrition