Depending on the distribution that you choose, a GUI is usually already installed, and will automatically boot.
It also depends on the distribution of your choice how to enable/disable the GUI. Usually you can, while in the GUI, press CTRL+ALT+F1/6, and a shell is presented to you, from there you can disable the gui.
Depending, again on your distro of choice, and the GUI delivered with it, you usually shutdown your GUI by:
/etc/init.d/kdm stop "OR" /etc/init.d/gdm stop
just to name an example.
If you don't want your system to boot in the gui, it depends on your distro, how to disable it.
So for more specific info, i would advice you to give us which distro you are using, or which you would like to start using.