You need to understand that the following command is just one way to create/open a file with an editor - here gedit
- using root permissions:
gksu gedit /usr/share/applications/sublime.desktop
Apparently, the tutorial you're following assumes you have these utilities installed and therefore you're getting troubles with that command. To do the exact same thing using more common tools, you could run the following command in a terminal:
sudo nano /usr/share/applications/sublime.desktop
This will open the file in nano
so you can insert text and save it with Ctrl+o and Ctrl+x.
sudo gedit /usr/share/applications/sublime.desktop
and type your sudo password and continue the tutorialAlt+Fn+F2
⌘ Cmd+Space
also see this