The amount of light reaching your sensor
You want your viewer to see all the details (highlights and shadows).
Whenever your lighting changes, you need to check the exposure.
Hold down the shutter button halfway
Look at the -3 > +3 light/exposure meter to see how your lighting is.
Positive number: overexposed (reduce ISO or add an ND filter)
Negative number: underexposed (increase ISO or add more lights)
To adjust exposure you can use:
ISO (light/noise)
ND Filters (camera sunglasses)
Lights
Sensitivity to light (like increasing the volume of a radio that has static)
Higher ISOs enable you to shoot in darker conditions but will show more of the grain or noise.
In general, you want to shoot with the lowest ISO you can.
Adjust your ISO until your exposure meter is on center (at 0):
Tap the bottom-right "ISO" number on your screen
Tap and drag to change the ISO based on your exposure needs.
If your light/exposure meter was showing a positive number: reduce ISO
If your light/exposure meter was showing a negative number: increase ISO
Neutral Density (ND) filters: sunglasses for your camera (use when it is too bright - overexposed)
Lights: (use when it is too dark - underexposed)