Lighting & Flash Photography

A couple of weeks ago, we had a whole class about flash and lightning, an essential part of photography. Unfortunately, I haven't been able to attend the class and as I was reading through one of my friends notes, I felt like I've missed quite a lot of important information about flash and as it is kind of difficult to understand everything just by looking at the power point or other people's notes, I decided that I'm just going to do some additional research on the topic.
I think that, first of all, one of the keys to understanding how flash photography really works, is understanding the main terms associated with it and thus I've just created a little vocabulary list to simplify things a bit:

TTL (Through-the-lens) Flash system - metering through the lens; 'measures the light reflected off 
the sensor / flim directly and terminates the flash at the correct exposure'
Flash 'sync' - the right timing of the flash to illuminate the whole frame
Shutter Speed - how long the image is exposed to light / how fast the camera's shutter opens
 -> a long shutter speed captures movement
Aperture - opening hole through which light enters the camera
 -> to work out aperture: take distande to the subject and divide the guide number by that distance, to get the 'f-stop' 
ISO (International Organization for Standardization) - the ISO number represent a film's sensitivity to
light; the higher the number the more sensitive the film is to light and thus it needs less light to get a good exposure
Flash to Subject Distance - determines the flash exposure, because of the power of the light emitted by the flash itself
 -> GN (Guide Number) - amount of light the flash bursts off (aperture x distance) 
     -> the higher the GN, the brighter the light emitted by the flash
 -> Inverse Square Law - when the light travels from the flash towards the subject, the intensity of the  light falls off quite significantly

Reading: 

David Präkel - Basics Photography Lighting