The second you decide to start using a speedlight (the flash) you enter a seemingly complicated world, the world of lighting. No are no longer accepting light as it is. You add, mould, redirect and create your own light. What follows is a simple outline of the logic behind flash photography.
There is only one assumption at this point: you have an external flash (speedlight or speedlite depending on whether you are a Nikon or Canon user) with a head that can be tilted and swivelled.