Außen is used to show that something is on the outside, on the outer side. You use it with sentences like: Das Auto ist außen schmutzig. The car is dirty on the outside. Draußen is used to show that something is outside of a room, in the open, outdoors. You use with sentences like: Die Kinder spielen heute draußen. The children play outside today.
I nearly put "Are they within or without?" but I'm pretty sure Duo wouldn't like it, though "within, without" are still occasionally used in the sense of "inside, outside" in British English, and in old nomenclature, for example "St John Baptist Without the Barrs" in Lichfield, UK. This was a hostel on the south side of the city for travellers who arrived outside the Barrs (city gates) after dark.