You may need to read the previous articles about cubemaps and framebuffers in order to understand this one.
The most common way to draw shadows is with shadow maps. Using a shadow map is similar to projecting a texture, but the texture contains depth data from the point of view of a light (located at the tip of the frustum).
This article is a work-in-progress. In the meantime, consider reading these other articles about the same topic:
The next article is about fog.