The X Window System provides the foundation for a graphical user interface. Prior to installing a desktop environment, a functional X server installation is required.
Install The X Window System
# apt-get install xorg
You will want to install GDM, KDM, or XDM to login with a GUI environment. GDM is the most popular but you can try the others
# apt-get install gdm
Install a Desktop Environment
The two biggest players in the game are Gnome and KDE, but there are also many smaller GUIs, like Xfce and LXDE that have just as much to offer. Install GUI on debian 7 wheezy
Start Desktop Environment
After installing a GUI (Graphical User Interface) or Desktop Environment, you can start to use by log in as root or non-root user.
If you messed up with the X Window System’s configuration, you can reconfigure the package as root
# dpkg-reconfigure xserver-xfree86
For Etch or Sid
# dpkg-reconfigure xserver-xorg