30A 220VAC will have 3 wires---2 HOT & 1 Neutral
30A 120VAC will have 3 wires---1 HOT, 1 Neutral & 1 Ground
To use that 220V in garage you would need to go back to AC Panel and take 1 hot wire off of a breaker and connect it to the GROUND bus. ID as ground by placing green tape around both ends of that wire (s/b a RED wire but not being code who knows)
In garage you should have 1 Black/HOT, 1 Red/was hot but now being used as Ground and 1 White/Neutral.
Wire nut appropriate wires (black/Hot, Green/Ground, Whote/Neutral to those in box and run to outside wall then into a Water proof 30A RV receptacle/box