nah Iso is film sensitivity. Keep it as low as you can (usually 100 or 200) as you get higher you'll get some "noise"
nah shutter speed determines the exposure's lenght
that's also why you need a tripod, stability for longest exposures, but you need one anyway to have 3 identical pictures.
basically you'll have these settings.
aperture (f number (f3.5 etc...))
shutter speed (1/500s to 30s depending on the camera)
sensitivity (ISO)
only one you'll need to change for exposure will be shutter speed (faster=less exposure, slower= more exposure)

original tuner ---- garage setagaya ---