Linux is a free Unix-type operating system originally developed by Linus Torvalds and other programmers in 1991 while Linus was a student a the University of Helsinki. He began writing the code based on minix and then released it to the public so that it could be improved upon. Other programmers in the spirit of GNU worked together to develop what we now take for granted, a derivative of Unix  designed to be fast, small, and reliable and most importantly free. 

Developed under the GNU General Public License,  the source code for Linux is freely available to everyone. Linux runs on many different hardware platforms including Intel, Sparc®, PowerPC, and Alpha Processors. Hundreds of application programs have been written for Linux, some of these by the GNU project. Linux's architecture like LNA creates a more reliable system. Systems using protected memory and pre-emptive multitasking are inherently more stable. 

Because the source to Linux is open source, it is easy to customize and to update rapidly (total cost of ownership is also low). This flexibility has enabled Linux to run on everything from handheld and embedded systems to clusters of hundreds of servers. LNA uses on the server side (Linbox NetServer) an industry- standard platforms running the Linux operating system.

At the heart of Linux is the kernel which basically runs the show. The Linux kernel provides the basic services and device drivers used by all other programs running on a Linux OS system. The latest kernels is 2.6.10.

Many tutorials on Linux Kernel are available at http://www.tux.org/lkml/.
    

Each distribution is developed with some unique purpose, and a number of factors should go while deciding which distribution is best for you. Some distributions are designed for home users, others are for commercial servers and clusters. 

In one line we can say "The best distribution is whichever one that You think is best according to your requirement". 

If you a newbie, I recommend Mandrake Official 10.1. The installations is very easy and the user interface is much more clean and practical than Windows. RPMs installation is easier than other distributions.

If you are not in a mood to install Linux on your machine, use the Live Distributions (SuSe 9.2 Live CDs, Mandrake Move Live CD or Knoppix 3.7).

Fedora and Debian Linux are widely used and you should go for either Fedora or Debian for all your need. It requires some time to master these distribution. You should work with distributions which form the base for most of the others, which at present are Fedora and Debian.