adds a start to the intro to the command line

.gitignore

@@ -0,0 +1 @@
+*.swp

essential/readme.md

@@ -319,7 +319,7 @@ You can verify the disk's content via the files explorer in gnome.
 Now, open a terminal and run the following.
 
 ```
-waldek@hellodebian:/media/cdrom0$ cd /media/cdrom0/
+waldek@hellodebian:~$ cd /media/cdrom0/
 waldek@hellodebian:/media/cdrom0$ ls
 AUTORUN.INF  NT3x          TRANS.TBL                          VBoxLinuxAdditions.run          VBoxWindowsAdditions.exe
 autorun.sh   OS2           VBoxDarwinAdditions.pkg            VBoxSolarisAdditions.pkg        VBoxWindowsAdditions-x86.exe
@@ -348,3 +348,67 @@ Once the machine is rebooted you'll can resize the window and the screen resolut
 You can also enable copy/paste and drag and drop between your host and VM now.
 
 ![full screen](../assets/VirtualBox_debian_18_02_2022_15_08_01.png)
+
+## Introduction to the command line
+
+We'll be using a few new *words* to reference the command line such as *shell*, *bash* and *terminal* through out the course.
+They all pretty much mean the same thing but with some small, and not so important, differences between them.
+Essentially a command line is a **textual interface** for humans to operate a computer.
+What is very important to understand is that textual command and graphical actions operate on the same computer. 
+For example, if you create a file via the command line, it will show up in you file explorer and vice versa.
+The graphical and textual interfaces are just different *representations* of the same machine.
+
+Now open up a terminal and you'll see the following.
+
+```
+waldek@hellodebian:~$ 
+```
+
+This is what we call a [prompt](https://en.wikipedia.org/wiki/Command-line_interface#Command_prompt).
+It's not much but it's our *window* into the computer.
+As with most things in life you can question it's *who, where, what and when*.
+This information is actually **embedded** in the prompt.
+Let's break it down.
+
+* `waldek` is **who** I am on this computer
+* `hellodebian` is the **what**, as in what computer I'm operating on
+* `~` is **where** I am located on this computer
+
+What about the *when* then?
+Let's type in `date` and see what happens.
+
+```
+waldek@hellodebian:~$ date
+Fri 18 Feb 2022 03:46:59 PM CET
+waldek@hellodebian:~$ 
+```
+
+There we see our **when**!
+But this miniscule operation illustrates us the **fundamental** operation of a command line!
+
+1. we have a prompt where we can run a program
+2. the program runs and outputs it's information on the terminal
+3. once the program **finishes** we can run an other program
+
+I'm deliberately saying program here but is `date` *really* a program?
+It's a bit basic no?
+Well, it is a program and most *commands* you'll type into your terminal are actually programs.
+We can illustrate this as follows.
+
+```
+waldek@hellodebian:~$ vlc
+VLC media player 3.0.16 Vetinari (revision 3.0.13-8-g41878ff4f2)
+[0000559c46ee95b0] main libvlc: Running vlc with the default interface. Use 'cvlc' to use vlc without interface.
+[0000559c46f89790] main playlist: playlist is empty
+
+```
+
+Vlc is now running and the terminal is *blocked* meaning we can't run other programs or commands in it.
+If you try to run the `date` command again, or `ls` or `htop`, it won't work!
+Try it out if you don't believe me.
+But what happens if you **close** vlc?
+The commands you typed get executed!
+This is an illustration of the **sequential** nature of a command line.
+
+
+