Debian is a free operating system (OS) for your computer. An operating system is the set of basic programs and utilities that make your computer run. At the core of an operating system is the kernel. The kernel is the most fundamental program on the computer: It does all the basic housekeeping and lets you start other programs. Debian uses the Linux kernel, a completely free piece of software started by Linus Torvalds and supported by thousands of programmers worldwide. A large part of the basic tools that fill out the operating system come from the GNU Project, and these tools are also free.
Another facet of an operating system is application software: programs that help get work done, from editing documents to running a business to playing games to writing more software. Debian comes with more than 1,500 packages (precompiled software bundled up in a nice format for easy installation on your machine) - all for free.
The Debian system is a bit like a pyramid. At the base is Linux. On top of that are all the basic tools, mostly from GNU. Next is all the application software that you run on the computer; many of these are also from GNU. The Debian developers act as architects and coordinators - carefully organizing the system and fitting everything together into an integrated, stable operating system: Debian GNU/Linux.
The design philosophy of GNU/Linux is to distribute its functionality into small, multipurpose parts. That way, you can easily achieve new functionality and new features by combining the small parts (programs) in new ways. Debian is like an erector set: You can build all sorts of things with it.
When you're using an operating system, you want to minimize the amount of work you put into getting your job done. Debian supplies many tools that can help, but only if you know what these tools do. Spending an hour trying to get something to work and then finally giving up isn't very productive. This guide will teach you about the core tools that make up Debian: what tools to use in certain situations and how to tie these various tools together.
Debian is an all-volunteer Internet-based development project. There are hundreds of volunteers working on it. Most are in charge of a small number of software packages and are very familiar with the software they package.
These volunteers work together by following a strict set of guidelines governing how packages are assembled. These guidelines are developed cooperatively in discussions on Internet mailing lists.