Table of contents :
First you need to install the Live Server plugin. The following picture shows my version, which is already installed. So there is no Install button, just a disable and an uninstall button.
When you start Live Server for the very first time, it is possible Windows Defender gives a warning. If that happens, just click Allow to proceed.
When you get a message saying something about invalid path, you have to check your live server settings to correct the paths.
When you start Live Server, it opens a browser window in the last window you used (your mouse was inside). So make sure that is the window you want, or open a new empty window before starting the server.
Make sure you have a main directory selected in the Editor, and make sure there is a default webpage inside that directory. That could be a very simple index.html file or any other file a browser accepts as a default webpage. (index.php or sometimes default.html or home.html)
When everything is ready you click on the Go-Live button. After that you see:
The url of your browser window will look like this: