1.  You would use external flash when there isn’t much lighting in the picture.
  2. No, you don’t need to meter the light because you have your own light.
  3. Flash synchronization means the opening of the shutter speed admitting light to photographic film or image.
  4. ETTL stands for evaluate through the lens and means that it is a type of auto flash exposure used by a canon.
  5. You will get black bands which means when your shutter curtain is blocking part of your image.
  6. They bounce the light and use a diffuser to soften the lighting.
  7. A slave in photography is a flash unit that fires when it detects the light from another flash unit.
  8. You can make your images lighter or darker with the aperture.