Understanding exposure is fundamental to photography I have below a diagram hopefully useful in making it easier to understand.
The values in the diagram are relative and different cameras have different ranges but the same effects will apply.
The 2 main settings to adjust exposure are Aperture and Shutter speed these are hard connected as below where the metered exposure is f5.6 for 1/125 second you can use any of the other values shown as the result will be the same
f2.8 for 1/500 second gives exactly the same exposure as f11 for 1/30 second
Aperture big (f2.8) gives a shallow Depth of Field small (f11) Gives a bigger DOF
Shutter Speed slow gives blurry moving objects whereas fast freezes the action
When you cannot get a correct exposure because of the ambient light then you can adjust the ISO and the triangle fulcrum balancing the exposure will go along the orange line either to the sun if bright or the moon if dark.
An excellent book is understanding exposure by BRYAN PETERSON