I'm not a server guy, but from time to time I have to setup a website for testing or development. Here are my steps for setting up nginx with PHP.

Installing nginx

Installing nginx is straight forward:

sudo apt update
sudo apt install nginx

Next is to verify that the firewall accepts nginx.

sudo ufw status

If "Nginx HTTP", "Nginx HTTPS", or "Nginx Full" is not listed you have to add the ones you need (Full is https and http).

sudo ufw allow 'Nginx HTTP'

Installing PHP

Using PHP with nginx requires PHP-FPM. If using Ubuntu 18, the repository must be added.

sudo apt-get update
sudo apt -y install software-properties-common
sudo add-apt-repository ppa:ondrej/php
sudo apt-get update