Can someone explain how DSLR scans work with film?

Looking at tutorials you backlight the film, get a macro lens and just take a photo, probably just my lack of much/any understanding but wouldn't this fuck with the film? I'd guess it would still be sensitive to light so having it out and lit to take photos would ruin it? I know there's a way to process film, but how would you do this at home? I don't have the space to set up chemicals or a dark room, and to make it I might as well buy a flatbed scanner.

Total newfag to film, only ever shot digi, please don't rape

Ta