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)