This time I would like to recommend some great sourcea of information for all my readers who like to use CLI applications on their lightweight Linux installations. As I have pointed out earlier, if you try to use Linux on a very old computer, you have to use some of your own brain power to compensate for the lack of a fast CPU and lots of RAM. Using the command line is one way to achieve this.
The Linux Documentation Project is the central site for all kinds of Linux documentation. In the tldp you'll find Guides, HOW-TO documents, and FAQs. Some of the files might be a bit outdated but even the older files provide the reader with plenty of useful information.
Gareth Anderson has written an useful summary of command line GNU/Linux applications. It is organized thematically, so that you can easily find the most useful tools for e.g. controlling processes and services, manipulating text files or working with the file system.
Michael Stutz's The Linux Cookbook: Tips and Techniques for Everyday Use is another good source of information with similar topics. It is a bit old (written in 2001), but the CLI tools don't change as fast as KDE and GNOME applications!
Machtelt Garrels has written a Bash Guide for Beginners. Bash is the default command shell of the most popular Linux distributions. This guide helps the newbie to write her first scripts.
After reading the Bash Guide for Beginners, you should continue with Mendel Cooper's Advanced Bash-Scripting Guide. It will probably teach you more than you'll ever need to know unless you plan a career as a Linux system administrator.
If you are willing to pay some money for books, you should seriously consider buying at least one or two books about the Linux command line. One good introduction to the command linux is Sander van Vugt's Beginning the Linux Command Line. In this book, you'll learn about command line basics, piping and redirection, using man to get help, administering the file system, partitions and logical volumes, working with text files, managing the users, groups and permissions and a lot more. This is probably the best book available now for any command line newbie.