This documentation accompanies each version of XFree86, and is available at the XFree86 website. Whenever you have trouble with your X environment, peruse the notes applicable to your videocard and chipset. These typically provide details about the configuration of the X Window System relative to your card, and will enumerate any "options" you have to include in theXF86Config file that governs X.
A great collection of pages is available at the Geek Girl.com website. Included are links to pages on the following:
Bash - The Bourne-again shell
Configure - used when compiling programs from source code
G++ - the GNU C++ compiler
Gcc - the C compiler
Libc - the GNU C library
Make - a program for directing recompilation
Note that some of these are included in the "docs" that come with Linux distributions. In general, these are detailed technical documents of particular interest to developers. However, if like me, you are not a programmer, you may peruse the introductory sections of these documents to get insight, for example, into those configureand make commands you use when installing applications from source code.
Many important programs that are frequently utilized by the Linux user are GNU utilities - for example, the tar (archive) and gzip (compression) programs. Descriptions of these programs are located at the GNU.org website where many Online Manuals may also be found.
These manuals typically provide a lot more information than is found in the corresponding man page on your system. For example , compare the man page and online manual for the tar utility.
The First Linux online guide has a nice collection of terms and definitions, sorted alphabetically. Go here if you encounter a term that you have not seen before or do not understand.
The PC Webopedia consists of a large online dictionary of computer-related terms and a search engine that provides links to documents that discuss each item in more detail. For example, I used this site to learn the differences between ISA and PCI buses.
The Topic Index to the voluminous hardware guide at PC guide.com will give you a great idea of the contents of this website. I used it quite frequently when first installing Linux and configuring the X Window System. I learnt a lot about videocards and monitors, including the concepts of screen resolution, color depth etc., useful when troubleshooting X display problems.