Emacs
Emacs is a powerful supported editor. It can be run in graphics or text mode.
To start emacs in gnome. Select Foot -> Damtp Apps -> Emacs Editor. or select the emacs icon for mthe toolbar. 
To start emacs in text mode, open a terminal or xterm window and type emacs.
Emacs comes with a tutorial. Open Emacs and select Help (from the top right hand side) -> Emacs Tutorial (first menu item).
You can use google to search for emacs tutorials.
There is more information at http://www.xemacs.org/ http://www.gnu.org/software/emacs/emacs.html.