I originally wanted to buy a SLR film camera, but I bought digital SLR camera photography skills. Is it useful?

There is no difference between an aperture and a shutter. You can read that book.

The digital ISO is the degree of film. The larger the value, the stronger the graininess, which means the higher the "noise".

To put it simply, portraits need a large aperture to blur the background and highlight the main body, such as 1.0, 1.4, 1.8, 2.0, 2.8 and so on. The set needs a small aperture. If you feel layered, you can choose 8, 9, 1 1, 16 and so on. Pay attention to choose a larger aperture and focus indoors, because the indoor light is limited. Outdoor shooting can adopt aperture priority.