Key/ Fill/ Back light
As the name suggests this is the most important light. Key light defines the shadows in a composition. All the other lights are placed according to the key light.
A fill light is used to open up the shadows. Ideally fill light doesn’t have its own shadow as it is generally less in intensity than the key light.
Kicker/ Rim/ Accent Light
Lights that outline the subject and separate the subject from the background. These lights are also known as side lights or hair light depending on where they are placed. These lights helps in popping the subject out. This light contributes to the lightest tones and specular highlights.
How To Set The Light?
1. Set The Key Light
Position the key light to define the shadows.
2. Add Fill
Add fill light depending on how much details you want in the shadows.
3. Look For Rim Lights
See if you can have a rim light from side or back which can add further to the image.
The ratio between the key light and the fill light. It is calculated as ratio between- Key+Fill : Fill. A 2:1 ratio means flat lighting where both sides of face are lit evenly.