GNU Emacs Manual

This manual is the most detailed and authoritative guide to using GNU Emacs. It tells you how to get started with Emacs, how to write simple messages as well as complex documents, and how to use special modes for editing, compiling, and debugging programs. It also explains how to handle multiple files and directories and multiple windows, and how to customize your environment.

It obviously cannot cover every add-on package available for emacs, but it covers some of the most commonly used packages.