By default the nouveau driver is used by Ubuntu for computers with NVidia Graphics Processing Units. While this driver works very well out of the box, some tools can not be used with the nouveau driver such as the CUDA 9 and 10 frameworks for machine learning libraries like Dlib or TensorFlow. For pure gaming purposes, the nouveau driver will work just fine.
If you want to run 3D games such as games from Steam but also still be able to do CUDA development you should install the binary video drivers in the Ubuntu repository.
Install Nvidia Proprietary Drivers
First we check and see if we have an Nvidia device. The [ubuntu-drivers] command will display all devices which needs a driver.
$ ubuntu-drivers devices
Using the autoinstall option Ubuntu will automatically install drivers for you.
$ sudo ubuntu-drivers autoinstall
This will install the 390 release Nvidia drivers.
$ sudo apt install nvidia-390