This adds the bumblebee repository to your software sources. You need this to see bumblebee and install it, because bumblebee is not coming with Ubuntu its third-party-software.
sudo add-apt-repository ppa:bumblebee/stable
This fetches the software lists from the sources, since you added a new source during the last step you have to update your lists by running this command.
sudo apt-get update
This finally installs bumblebee. And yes, the other steps are necessary.
sudo apt-get install bumblebee bumblebee-nvidia
No it is without any GUI. But in my opinion you won't need one anyway ;P
as it says If you are on Ubuntu 11.04 or older ... and you are not, so you can ignore this step:
sudo add-apt-repository ppa:ubuntu-x-swat/x-updates