When materials are cooled their molecules vibrate less and compact together. When most materials reach a temperature called the freezing point, the molecules form a crystalline solid - although some materials (like glass and tar) do not crystallise at all but form super stiff fluids, which seem to be solid. Only Helium will not freeze; all other substances will freeze if cold enough, but fluids like cooking oil, antifreeze, petrol (gasoline), nitrogen, etc. freeze at temperatures that most people don't experience.