Do _not_ install by hand.
If you really want to install by hand,
even though it will break things as you don't seem
experienced with Linux:
the root account is deactivated / without password
in Ubuntu, so you either have to use sudo
or set the root password (not recommended) with sudo passwd root.
Please read the post above and act accordingly.
You can install the driver by using ubuntus package
management, depending on your card either
nvidia-glx, nvidia-glx-new or nvidia-glx-legacy.
those can be installed with sudo apt-get install <drivername>
or, if you don't want to do this by hand, by using
the application "envy"