The Source engine is a 3D game engine developed by Valve Corporation. Its unique features include a large degree of modularity and flexibility, an artist-driven, shader-based renderer, accurate lip sync and facial expression technology, and a powerful, efficient and completely network-enabled physics system.
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.
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.