i grew some sunflowers indoors but now they are getting really big should i plant them out doors and if so how

Yes- plant them outdoors ASAP in a sunny spot and water them in well. They will take a week or so to get over the shock of transplantation then they will really take off and you should have flowers within a couple of months. Really tall varieties often need some support (bamboo canes/stakes) so that they don't collapse in strong winds.