Area Lights
The main usage for area lights (in order to answer to a very frequently asked question by many beginners) is achieving shadows with soft borders. But they are also useful for simulating the lighting of a supermarket, a computer screen or a cloudy outdoor....
The Spotlight
This tutorial is all about generating shadows (which is pretty easy) and making them look the way they should (which can become very intricate).
Ambient Occlusion
Global illumination is a very popular method for lighting three dimensional
scenes. Unfortunately, most of the methods are very slow and requires lots of ressources. Ambient Occlusion is a method for simulating global illumination, while keeping a respectable ratio between results and computing times.