Over a hearth. They would have used pots, or baked meat and tubers (like potatos) with hot stones. This video gives you a good idea of ways prehistoric people may have cooked:...
They Buried them under ground that's how they refrigerated there items but they stored food in Makeshift larders
They had farms ( crops ) and made them to have food .
They hunted and gathered food so they hunted animals and gathered plants
I'm pretty sure they hunted for their food... if not they probably ate stones ha