The perfect exposure all comes down to the exposure triangle, which is made up of ISO, aperture and shutter speed. Having the camera settings in the middle of triangle at 0 on the char will make make the image have an even amount of light.
In this image, the first image has a low ISO, making the image clear, and in terms of the exposure triangle, the settings have been set at 0 on the scale, making the exposure looks even. the second pictures ISO has been set in the middle, which means it will be more sensitive to light, therefore i changed the aperture to a lower setting to not let as much light in. On the last image, i set the ISO to really high, but didn’t change the aperture, therefore its gone really bight and the exposure is too high.