If you want to install the Nvidia driver Nvidia in Ubuntu you can follow one of this guides (according to the release of Ubuntu which you are using):
NOTE: if you have no idea of which version of Ubuntu you are using, type:
which will give you something like this:
Another way to install the latest version of the Nvidia driver is that of using my script "Envy":
NOTE: Envy is not supported by Ubuntu in any way and you should use it at your risk.