A level which will be compiled into a BSP is build with many different kinds of objects.
With this tutorial the author intends to introduce these objects to the reader.
This is an advanced, detailed quality tutorial about the legendary id Tech 3 engine's renderer technique. Written for all interested casual readers, provided as de-tech-termed simplified English document.
Finally, a mapping-for-dummies tutorial. Thanks to the author. :)
It is not a mapping tutorial :P , it explains the technological architecture behind the mapping process.
There are hundred of mapping tutorials, and this document shall be considered as additional literature to any mapping tutorial telling you how to do nice mapping.