Nginx.conx Configuration of nginx reverse proxy, especially fastcgi

There is an example nginx.conf file in the docs.

This example has

include fastcgi_params;

Where do I get these?

And how does the php-handler work?

upstream php-handler {
    #server unix:/var/run/php/php7.4-fpm.sock;

Can someone share a configuration for a reverse-proxy? It would be also nice to split the nginx.conf because I have several applications running on that server.