It is considered that Linux is very hard to learn. In a certain point it's true. Why? Because Linux is other than Windows - these are two absolutely different operating systems. Remember the first time when you saw the computer with windows? I don't think it was easy for you to get used to it. You'll have to learn how to use Linux from the very beginning, and that's why it's hard, just like the first time you saw computer.

This quite short article will only introduce you to Linux, you'll learn here only what is needed, for the beginning (though a lot of people managed to learn it without any helping manuals).

Now I guess you are a newbie right now, otherwise you won't read it. 'Kay. you have to choose a Linux distribution, as there's a lot of them out there: OpenSUSE, Mandriva, Debian, Ubuntu, Slackware, Arch, Gentoo and many other. What shall I recommend to you? I'll strongly recommend to you you use Slackware. Not just because I like this distribution, but because it's the most logical choice there. First of all: what do we want, in the way of a hacker? Understanding the System. I'd better stay out of philosophy right now, so let's speak about computer system.
Why can't we reach full understanding of operating system with Ubuntu, OpenSUSE, Mandriva, also Windows? Because this are so-called "clicking" distributions: here you use your mouse, you click the buttons, and the program is configuring everything for you. This have its advantages for a office use, but not for us: like I said, we want to understand how system works, which is too hard when everything is done by computer, and secondly, automatic configuration produces an errors, and skips them, without proper solution. This leads user to different kinds of errors, malfunctions. In Windows - to the Blue Screen of Death. That's why Slackware brings you combination of opportunity to learn Linux and stability.
There are some other advantages of using Slackware, for example it's not a commercial distribution, which doesn't lead us to the problems with copyrighted software, like mp3 and video codecs. No matter what others say, Slackware is easy to use. It has nice tools for system administration, which allow you simple network configuration, package administration e.t.c. You can change Slackware to whatever you want, once you'll become more advanced in this stuff.
These are some of a reasons, why I use Slackware, and why I recommend it to you.

Alright, enough Slackware propaganda, let's get to work. I will not tell here about specific distribution tools, I'll tell about basic things in Linux. If you want more information on Slackware, check out main web of Slackware: http://www.slackware.com or download the Slackware book: http://www.slackbook.org .

1. Linux filesystem

We know, in Windows, to each partition are assigned letters (C, D e.t.c.). These are starting directories. In Linux it's different: there's only one starting directory, marked with "/", named 'root directory'. If we'll take a look at the files in / directory, we'll see here directories like etc, bin, home, usr and others. Each of them have it's own function, and each of them can be placed to the different partitions. Can you imagine C:windows and D:windowssystem, being on the same machine?
For the partition to be accessible, it must be mounted. The system must be "told" the device, where the partition is situated, and the directory where it's files will be listed - a so called "mount point". To better understand this kind of stuff - we installed Linux, we had two partitions. One was clean, another had Windows. We installed Linux on this clean partition. Now, when we launch Linux, this partition is a root partition - /. We want to make our windows partition make accessible. We have to mount it. In the special configuration file (/etc/fstab) we input the device of this partition, for example, /dev/sda1 (we'll talk about devices later), a mount point - /windows, a file system - ntfs, and few other parameters. After we mount it with a special command, in our root directory we'll have a windows directory. If we open it, we'll see contents of a windows partition.
Also, as you might have guessed, we use frontslash / in linux, instead of backslash, used in windows. New users should remember, that Linux is case sensitive. If we want to access file /home/user/Desktop/document, we must write the address like that, and if the address will be /home/user/desktop/document, you'll get the error message.
Now let's take a look at the directories in the /root partition. If we'll take a look at the / directory, we'll get at least the following:

bin/ etc/ lib/ mnt/
proc/ sbin/ usr/
boot/ dev/ home/
opt/ root/ tmp/ var/

Each of these directories have their own purpose. Let's take a look at some of them.

/bin - contains executables, used both by administrators and unprivileged users. There are such executables, as "bash", "cp", "ls", "mv".
/etc - contains configuration files of your system
/lib - here are all shared libraries, required by different programs
/mnt - a mount point for different media. however, it can be changed
/proc - the /proc filesystem is a pseudo-filesystem, that, in fact, doesnt exist on any particular media, but in the virtual memory. It's purpose is to mantain dynamic data of your system.
/sbin - contains executables used for system administration
/usr - probably most important system directory, asit has all user executable files. support libraries for X are also kept here.
/boot - contains files used by bootloader, and a linux kernel
/dev - in linux, everything is files or directories, which means devices are also files - you can get data from devices (equivalent to reading files), and send data to devices (equivalent to writing files). For example, cdrom file represents you cdrom device, fd0 - your floppy reader. A very bright example is /dev/dsp - a speaker. You can write to this file, and you'll hear a sound - data are sent to the sound card. For example, you can "listen" to linux readme file, by inputting the following command: cat /usr/src/linux/README > /dev/dsp .
/home - in this folder are created user folders - each user has full write permissions to his folder. User configuration data are stored here.
/opt - this is a directory for installation of a software, that's not the part of a default installation
/root - a home folder of a user root
/tmp - directory for a temporary files
/var - contains such things as received mail, different system logs e.t.c.

2. Commands

Now that you know general things about filesystem in linux, let's now take a look on how can we manipulate with files and perform different tasks under Linux, yet, not using graphical environments. Now, we will learn some things about linux commands.
I'll write here main commands and explain what do they do, and how to use them.

cd <location> : command for changing current directory. you can input absolute path, for example /home/user/Documents, or relative path: Documents (assuming your current location is /home/user). to change location to the upper directory with a relative path, just input location ../ (e.g. cd ../)

ls <location> : command for listing files in directory. you can input just ls, so files in the current directory will be listed, or you can input absolute path. Another thing to mention are wildcards, for particular file matches: if we input command ls /usr/bin/p*, we'll get listing of all files, whose filenames are starting with p, if we input ls /usr/bin/*yt*, we'll get all files, whose name have yt. Here, wildcard * means "any".

cat <filename>: command for displaying file. you can input relative path of a file, you want to display, or a full path to a file. This thing is good, if your file isn't big, as you won't have possibility to scroll through the console output always, I'm talking about text mode now (we'll talk about it later). In case you want to view bigger file, you can use "more": for example, more /usr/home/tetxfile. textfile will be displayed in something like pages - press spacebar for next page.

mv <oldlocation><newlocation>: moving files. first input oldlocation of the file, then input location location of a new file. Locations can be relative. Exmaple: mv /home/user/doc1 /home/user/newdoc. mv is also used for renaming files.

cp <oldlocation><newlocation>: works like mv, except it leaves oldfile, and in a new location, creates a copy of a file.

mkdir <location> : will create new empty directory

rm <filename> : will remove file. Just remember, that it doesn't remove directories.

rmdir <param> <directory> : without parameters, will remove directory, if it is empty. If directory is not empty, use -rf parameter. Use with caution.

clear : if you got too much garbage in your console, you can clear it with this command.

man <command> : get detailed help on using a recent command.

nano <filename> : nano is a basic editor for linux. You can open existing files with it, or create a new files, by inputting a unique filename. Once nano is opened, you'll see possible options in the bottom of a screen. ^ means Ctrl button.

vim <filename> : advanced text editor. you can edit existing file, by inputting it's name after command, or create a new file, by inputting a unique filename. Once VIM is opened, press I to start editing. You can get VIM command line at any time by pressing Esc + :. To write a file, input w!, to quit q, to quit without saving use q!. more info in the VIM documentation.

./<filename> : with this command, you can execute file. For example, you got a script shell.sh, and you want to execute it. Type ./shell.sh to execute it. Filename path can be absolute or relative. Note that to execute files, they must have execute permission. See chmod.

chmod <parameters><filename> : change permissions of a file. You can define what permissions you are giving to a file with parameters. Here are some of them:

400 read by owner
040 read by group
004 read by anybody (other)
200 write by owner
020 write by group
002 write by anybody
100 execute by owner
010 execute by group
001 execute by anybody

lynx <url> : though, this program isn't installed in every distribution by default, I'll mention about it, as it can be very useful sometimes. lynx is a text web browser, it doesn't show images. It doesn't support frames or tables, it's a very simple text browser.

links <url>: another textbrowser, but a little bit more advanced. it supports tables, and have some useful functions.

3. Text mode, X Window System and KDE

First of all. Normally, there's a text mode, where instead of pixels are used symbols - text. Of course, here you can't see any graphics, which means you can't view images, you can't launch application that are created for a graphical mode. However, textmode is good for a specific work. For example, you'll really appreciate a black background with a gray text on it, when you've been working with a code the whole day and night.
When you are in text mode, you can switch between virtual console using Alt+F#, where 3 is a number of a virtual console (1-6). You can do some configuration using command setterm. You can get more information on using this command simply by inputting it without any parameters, or, for more advanced help on the command, see man pages (command "man setterm").
To switch to a textmode when you are in graphical more, use command "telinit 3" (for this, you gonna need root privileges). To get back to the Windows System, input "startx".

Now let's take a look on the X Windows System. Like it is written in Wikipedia, "the X Window System (commonly X11 or X) is a system which implements the X display protocol and provides windowing on bitmap displays. It provides the standard toolkit and protocol with which to build graphical user interfaces (GUIs) on most Unix-like operating systems".
X Windows System is provided by the X Server. I wouldn't better explain now the configuration of an X Server, usually it is configured automatically. To launch an X Server from a textmode, input command "startx". Here will be launched default graphical environment, that you've probably selected during installation. Here comes X, differences between distributions, here come problems. Different distributions have different configuration tools, different default graphical environments. Better take a look at your distribution manual to see, how to change configuration of different X stuff.

In the beginning of this article I was talking about Slackware. In Slackware, the main graphical environment is KDE. Currently, KDE is most popular graphical environment (second most popular is GNOME), and it is known as easily-configurable environment. Here, you don't need to change any configuration files manually, but you can use such a things, as Control Center and others. Let's take a brief look at the main applications in KDE.
But before we do, I would like to mention that you can execute programs quickly, by pressing Alt+F2, and inputting a command.

Konqueror (execution command: konqueror) : a multi-purpose program: a file manager, a web browser. Has built-in KIO, for support of such things, as FTP.
Kwrite (command: kwrite) : a simple KDE text editor.
Kopete (command: kopete) : a KDE communication program, supports such protocols as ICQ, AIM, Jabber, Yahoo, IRC and some others.
Konsole (command: konsole) : terminal emulator for KDE

You can find a lot more K applications, by looking at the K Menu.

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Further reading:

Slackware book - http://www.slackbook.org/
Linux shell programming - http://www.freeos.com/guides/lsst/
Other free books about Linux - http://www.linux.org/docs/online_books.html