If we change aperture..does it affect on lighting conditions? Or only shutter speed affects light..?
Basically, to affect the exposure, there are three parameters, often called the exposure triangle. They are composed of the aperture, the shutter speed and ISO. You always have to make a compromise between the three of them. The aperture is a division (f/2.8 (in which "f" is the focal length)) which means that the smaller the number, the bigger the resulting aperture. That means, more light coming to your sensor and less depth of field. Put simply, it's a bit like the size of a garden hose, 1/2.8 would let more water (light) through it than 1/16.
Furthermore, it's always good to know your stops when you take photos (1 stop means double or half the light). The stops for shutter speeds are easy : 1/60 is one more stop (double the light) than 1/120. For the aperture, they are harder to remember: f1.4, f2.0, f2.8, f4, f5.6, etc. So, let's say you have an exposure at 1/60, f4 and iso 100. If you want the same exposure, but with a faster (bigger) aperture or a faster shutter speed, you could make it : 1/120, f2.8 and iso 100.
If you need more details, you can look online for the exposure triangle. Here is one link : https://fstoppers.com/education/exposure-triangle-understanding-how-aperture-shutter-speed-and-iso-work-together-72878
I hope that answered your question!
Aperture and shutter speed both both independently change the amount of light passing through the lens/camera to fall on the the sensor or film. ISO changes the sensitivity the camera has to the light passing through the aperture and shutter.
Changing the ISO does not change the amount of light passing through any given set of aperture/shutter speed combos. It ONLY changes the sensitivity, or the amount or light that is required, to achieve the correct exposure for the conditions you are photographing in.