Mens Designer Shirts

Want a nice new shirt? Then why not choose the best around? Choose Armani and you won’t regret it, not only are they well known for their high quality mens clothes but they also make some very nice shirts, this white one is made entirely from high thread count linen which makes it extra soft and comfortable.Im a freelance graphic designer for bands and i mainly do web stuff. I’m becoming interested in doing shirt designs and there is one thing i dont understand. Is it the designers responsibility to make sure that the colors are all separated or is it that of the printer?
Am i supposed to just send a high res version of the design to the band and then the printer takes care of the rest?
any help would be amazing!thanks