do you mean a film camera or a digital camera?
with a film camera you change the film to high ISO (which is called “fast” film). 400 was “fast” film, I used to use it a lot when taking “normal” photos as I was in indoors in dark squats and disused buildings.
with digital cameras, even cheap ones now have 1600 or 3200 ISO. My mum said I could keep the compact one she got in Malaysia when she went back (they are more advanced than England when it comes to cameras), as it had higher ISO, it can go up to at 3200. some cameras allow even higher but with less resolution.
when you use high ISO you don’t need flash as often but there is often “grain” (extra stray pixels) like old film had more grain when you made it “faster”. you can slightly blur these out on photoshop and then it looks more like old film than a cheap digital camera.
