Gedit, the default GUI editor if you use Gnome, also runs under KDE and other desktops. Most gNewSense and Ubuntu installations use Gnome by default. To start Gedit open a terminal and type
$ gedit &
You should see this:
This looks like most basic editors on any operating system. You can use Gedit through the GUI, and the commands are simple:
File->Open : Opens an existing file
File->New : Creates a new (blank) file
File->Save : Saves a file
ctrl + c : copy
ctrl + v : paste
That's all you really need to do. To add text just type!
Gedit tracks your cursor and displays the position at the bottom of the interface:
This can be handy information to know. If you keep track of the line numbers you can use these to jump quickly around the text file by using the "Go to Line" feature. This can be accessed via the interface (Search -> Go to Line) or via the shortcut ctrl + i.