Notices

The name pretty much sums it up. I have no clue what x terminal is. Can someone help me out?

its in your utilities, and is the way you enter commands, in the command line if your familiar with that sort of thing

If you prefer the windows approximation, it's like the "command prompt" (pretty similar, at least).

I don't think that's a very thorough answer to the OP's question.

You are just going to have to search for articles on learning to use Command Line Interface. If you've ever used DOS or MS Command Prompt then it's something like that.

Many articles such as this exist: http://www.downloadsquad.com/2008/01...-the-terminal/

Linux has an emphasis on CLI, you can do almost anything from the command line and most things are more efficient from terminal than a graphical approach.

You may want to play around with a Linux Live CD on a desktop/laptop as xterm uses busybox (limited default commands, lots stripped out). You should also know that there is a certain amount of Tab completion (tap the tab "button" a couple times).

ROXterm and packages such as bash3 may also be useful.

As OS 2008 is based on Debian and Ubuntu is based on Debian (Mer is merging with Ubuntu MID) the common code base and structure allows you take advantage of forums such as ubuntuforums.com for tutorials.

The basic things you should learn are:
cd - change into a directory. For example cd /home/user/
ls - list contents of the current directory/folder
cp - copy a file.
cp -R copy a folder
mv - (be careful) move a file or directory
ssh - connect to a linux machine. ssh root@192.168.1.100 for example
scp - uses ssh to copy over a network. scp /home/user/file.txt root@192.168.1.100:/media/
df -h lists partitions and disk usage
du -sh disk usage of directory. du -sh * disk usage of each file or folder within a directory.
apt-get install package install software from CLI. (need to be root)

Does anybody knows where I can find some tutorials or ebook or anything to learn X-terminal from?

X-terminal is simply an interface so no actual tutorials for it. There is a Wiki page of Shortcuts

A google search found the following link that might be useful: http://wiki.eeeuser.com/explain:terminal

Note to any Wiki editors: Worth considering having a similar page in our Wiki.

You can learn the basics here: http://www.freesoftwaremagazine.com/...intro?page=0,0

However not all the commands listed there will work on your N900 (for example the man pages are not installed to save space)

X terminal is just one way to interface... search for howto use shell shell utilities and so on

simple if u wanna compare it with ur pc, u'll find it somehow quite similar to the MS Dos as commands, with some deferences (such as case sensitive).
however, as the other gentlemen mentioned, u'll not need it always.. or let's say, u still can survive without it..
good luck..

Yours isn't either! You do not even mention a single answer to the above question!

BASIC:
x-terminal is a program to display the command-line-interface (also referenced to as CLI or text-shell) in a GUI (graphical-user-interface) environment (thats the desktop you see and can click on).

DETAIL:
A shell is actually providing an interface to the system.
A shell providing a text-interface (ash, bash, ksh, ...) is called CLI and providing a graphical-interface (windows explorer, kde, gnome, ...) is called GUI.

In N900's case the provided text-shell is ash, that can be changed if needed.