The instructions to disable xdm/kdm/gdm/whichever-dm-you-have is correct. If you don't do this, you boot to a graphical login (that's the dm = display manager), and then whenever you quit X (which should be as easy as ctrl-alt-backspace -- try it, but close your apps first), the DM will respawn another graphical login, making it impossible to escape the GUI.
Another possibility with debian is to check in /etc/rc[N].d for a runlevel which does not start the dm, and make that the initdefault in /etc/inittab. I don't have an unmodified debian system at hand, so I can't say which if any that will be -- possibly 2. Do not choose 0, 1, or 6.
Once the dm is disabled, you boot to a login console. From there you can start X with the command startx. This includes a default DE and if you've been using gnome that will probably be it. You can also create an ~/.xinitrc, which is a shell script which will be run in place of the default. Generally they can be pretty minimal, eg:
#!/bin/sh
exec gnome-session
Should start gnome (I believe -- I don't have a gnome system at hand either).
Note that you can't run a GUI application without X; it's not clear from your post you understand that. GUI programs are actually clients that need the Xorg server to work. You can start a bare X with no DE or WM and a specific application by replacing the exec gnome-session line with the name of the application, but beware you'll then have no way to start anything else and when you close that application, you'll be looking at a blank screen with a cursor floating in it.
There's nothing dangerous in all this and it is easy to re-enable the DM if you want.
Best Answer
command is "deja-dup-preferences" just create a menu item on whatever desktop you are using that executes the above command and a GUI will open up on your desktop