Shivering is a body reflex that attempts to keep the body warm when in cold conditions. The muscles around your core start to shake, i.e. it’s your body’s reflex to warm itself up by moving or releasing energy.
I don’t know how effective it is… since by shivering you are releasing heat from your body the environment around it.
Usually it’s a good sign hypothermia is on the way if you’re in extreme conditions, so get your body inside & warm. 🙂