If you're using an NVIDIA graphics card and you want to use the proprietary drivers instead of the open source Nouveau drivers, there are a few things you need to do. First, make sure that your system is up-to-date by running the following commands in a terminal:
sudo apt update
sudo apt upgrade
Once that's done, you can install the NVIDIA drivers by running this command:
sudo apt install nvidia-driver-390
This will install the latest driver for your NVIDIA graphics card. If you want to install a specific version of the driver, you can replace 390 with the desired version number. For example, if you wanted to install version 340 of the driver, you would run this command instead:
sudo apt install nvidia-driver-340