1. to turn off, to switch off (There are other options like "ausschalten" but this one is by far the most common in daily life.)
How useful:
Opposite (closest): anmachen
2. to make out (distinguish, recognize) (Rarely used, but it's a parallel to English.)
How useful:
3. to agree (on something with someone) ("etwas mit jemandem ausmachen" - in the sense of finding an appointment or a some sort of contract. NOT for agreeing to someone's opinion.)
How useful:
4. to faze someone, to mind, ("jemandem etwas/nichts ausmachen" - think of it as "be a turn-off to someone", but it's not as colloquial sounding.)
How useful:
5. to have a (big) effect, make a/no difference (Usually used in combination with "viel" or "wenig" or "nichts")
How useful:
6. to define, to make (Usually in the phrasing "X macht Y aus." - "X is what makes Y.")
How useful:
