Quickly Type Special Characters Ubuntu

Here are 3 simple ways to search, insert & quickly key in special characters in Ubuntu.

1 - Use KCharSelect / Character Map
Character Map is pre-installed in Gnome Desktop & located at Application > Accesories > Character Map.

Press Ctrl+F key to search special character
Simply double click, copy & paste any special character you want to use.

Gnome Character Map

KCharSelect

KCharSelect is pre-installed in KDE.

For Gnome users, use this line in Terminal to install:

sudo apt-get install kcharselect

After installation, go to Application > Accesories > KCharSelect to run this tool.
Same as Character Map; double click, copy & paste any special character you want to use.

2 - Compose Key Mode.
Ubuntu also has a composition table, a mapping from sequences of keys called key chords to individual special characters. The composition table for Ubuntu can be found here https://help.ubuntu.com/community/GtkComposeTable. For frequent use of special characters, composition shortcuts is a faster alternative. This mode can be applied on most text boxes in Ubuntu ( OpenOffice, GIMP, Gedit, Firefox, etc )

Set Composition Key

Go to System > Preferences > Keyboard
Select Layout tab
Click on Layout Option
Click Compose Key position
Tick any key you want to assign as Compose Key ( in my case : Right Alt key - image )

Assign Compose Key

How to use?

Press 2 combination key after Compose Key

example : © ( Copyright sign )

Press & release Compose Key ( in my case : Right Alt key )

Press o key

Then press c key

[ compose key + o + c = © ]
Special character © should appear

3 - Unicode entry mode
This mode same as Compose Key mode but with different activation key combinations. This mode also can be applied on most application text boxes.
You can find Unicode number or key combinations from Character Map or KCharSelect(see image)