Fog Lights only, Low Beam only or Fog Lights + Low Beams.
In fog you should use dipped headlights or front fog lights. Also you should use high intensity rear ( fog) lights.
Low beam headlights and fog lights if the vehicle has fog lights.
When its foggy or a snowstorm
Low beams and fog lights if equipped. High beams only light-up the fog more.
Fog lights
Low beams
low beam
Use the low beams if your car is not equipped with fog lights. It's never recommended to use high-beams in fog, as it makes it about 4x harder to see, and makes the fog look denser.
in the fog
Low beam or fog lamps only.
There isn't really a distance when you should use your fog lights, Switch on headlights, dip them if necessary and turn on fog lights if visibility is reduced. Fog lamps are very bright, however, so if you can see the vehicles behind you then it's likely they can also see you. In this case your fog lights will dazzle other drivers so turn them off
Adjust your speed to condition, use only your low beams (and fog lights, if so equipped).