How does xdebug debug work on a remote server?

Question

xdebug

Explain how a locally installed xdebug works with a remote server? I need to set up a config in VS Code, but without a general understanding of the principle, it will be difficult at all ...
In the man'e for configuring xdebug, I found a format entry:

// server -> local
"pathMappings": {
  "/var/www/html": "${workspaceRoot}/www",
  "/app": "${workspaceRoot}/app"
}

ps I also do not understand how to configure the config for scripts run in cli mode