In this section, I provide a number of links to websites that I have found useful while learning to use Linux. This is an eclectic collection, but keep these handy.
Depending on the X Window Server your distribution is using, you will need to look at either the XFree86 website or the X.Org Foundation 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 the XF86Config file that governs X.
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 FSF Free Software Directory 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 Free On-line Dictionary of Computing (FOLDOC) is a huge encyclopedia of computing terms and concepts, maintained by Denis Howe. It has very detailed articles, with a lot of cross references. It's a very good reference to understand anything related to computing.
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.