FOSSwire have posted a PDF “Ubuntu Cheat Sheet,” covering the basic terminal commands one might have to use and, just as importantly, naming important programs and packages.
With “Ubuntu Cheat Sheet”, you don’t end up deleting or messing with something that’ll cause headaches down the line.
You can learn how to use Ubuntu with command line
Ubuntu Cheat Sheet [FOSSwire]

Gajim is a free software, instant messaging client for the Jabber (XMPP) protocol which uses the GTK+ toolkit. It runs on GNU/Linux, BSD and Windows.
The name Gajim is a recursive acronym for Gajim is a jabber instant messenger.
The goal of Gajim is to provide a full featured and easy to use Jabber client. Gajim works nicely with GNOME, but does not require it to run. It is released under the GNU General Public License.
Gajim should not be confused with Gaim, another instant messaging client.
Features

Tabbed chat window
Group chat support (with MUC protocol)
Emoticons, Avatars, File transfer, Room Bookmarks
Metacontacts Support
Trayicon, Speller, extented chat history functionalities
TLS and GPG support (with SSL legacy support)
Transport Registration support
Service Discovery including Nodes
Wikipedia, dictionary and search engine lookup
Multiple accounts support
DBus Capabilities
XML Console
Gajim is available in 22 languages: Basque, Belarusian, Brasilian, Breton, Bulgarian, Chinese (simplified), Croatian, Czech, Dutch, English, Esperanto, French, German, Greek, Italian, Norwegian (Bokm?l), Polish, Portugese, Russian, Spanish, Slovak and Swedish

Installation
You need to add Ubuntu universe repository, then use the command line and type:

apt-get install gajim

Happy Chatting and have a great day!