You have to install X windows. http://www.x.org/
Then you have to install any of the GUI interfaces you like (GNOME, KDE, FLUXBOX...)
I don't really know how to install these from source, because I have never done it. But it should probably go like any other program being installed from source with unpack, ./configure, make, make install.
These are all just programs, so they shouldn't interfere with the command line you are running now.