Learning even just the basics of photography takes a bit of work and one of the more complex ideas is the relationship between ISO, aperture and shutter speed. Lifehack has a graphic that helps make sense of it.
The graphic does a reasonable job at explaining how the amount of light you let it affects a photo, how certain settings can increase noise, and how focus changes. The top represents aperture, the middle ISO, and the bottom different shutter speeds. It's not a perfect representation of exactly what you'll get, but it's a nice visualisation that helps you understand the basics.