In Ubuntu, the default driver for NVIDIA GPUs is an open-source driver called Nouveau; unfortunately, this does not work with CUDA at all, so we will have to install a proprietary driver. We will have to add the special graphics-drivers repository to our package manager to be able to download proprietary NVIDIA drivers to our Ubuntu system. We add the repository by typing the following line into the bash prompt:

sudo add-apt-repository ppa:graphics-drivers/ppa

Since this is a sudo superuser command, you will have to enter your password. We now synchronize our system with the new repository by typing the following line:

sudo apt-get update

We should now be ready to install our driver. From the Ubuntu desktop, press Windows + R, and then enter software and drivers:

The Software & Drivers setup menu should appear. From here, click on the tab marked Additional Drivers. You should see a selection of available stable proprietary drivers for your GPU; choose the newest one you see I(n my case, it is nvidia-driver-396, demonstrated as follows):

With the latest driver selected, click on Apply Changes. You will be prompted again for your sudo password, and then the driver will install; a progress bar should appear. Note that this process can take a long time and it may appear that your computer is hanging; this process can take well over an hour, so please be patient. 

Finally, when the process is complete, reset your computer, and return to your Ubuntu desktop. Now type Windows + A, and then enter nvidia-settings (or alternatively, run this program from a bash prompt). The NVIDIA X Server Settings manager should appear, and indicate that you are using the appropriate driver version: