Making an exposure is something we do with our camera.
An exposure is a recording of light onto light sensitive material. Light sensitive material can be film, a digital sensor or even the photographic paper that is used for making prints.
Exposure is a combination of aperture (f-stop) and shutter speed.
ISO refers to light sensitivity. We describe the light sensitivity of light sensitive material with an ISO number.
Tonality is how we describe the brightness of our picture.
The tonality of our photograph can be controlled by exposure and light sensitivity.