VNC is a system that allows you to remotely control another computer. It allows you to relay your mouse and keyboard inputs as if you were physically sitting in front of the system, when in fact you could be on the other side of the world. It works well for sharing your desktop screen with another user, whether you want to grant them the ability to control your computer or just be able to see what you are doing on it (with mouse and keyboard input blocked).
This is a companion discussion topic for the original entry at https://linuxconfig.org/share-your-desktop-screen-with-vnc-on-linux