1. Important factors to consider when shooting a portrait are to make sure that you have the light and subject at certain angles so there is not too much shadows and more light.
2. The difference between broad and short lighting is that broad lighting gives off more regular light than reflective light and short lighting gives off more shadows and the reflection bounces off the opposite side of the shadows.
3. The function of the main light is something normal, light reflecting off the front of the face.
4. The function of the fill light is adding more light to the shadows.
5. The function of the background light is adding an extra light to the background to give off a small flare as assistance.