“PHP is a programming language you can use to create web applications. It's free, powerful, relatively easy to set up and learn, and it has extensions and frameworks available to do almost anything you could imagine.” - Excerpt From: Alan Forbes, The Joy of PHP
In order to write PHP programs you are going to need to install PHP and composer (a dependency manager):
# on Linux
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install php
sudo apt-get install php-cgi
# on MacOS
brew install php
brew install composer
# Spin up a local server to run your PHP files
php -S localhost:8000You may also opt for a a complete AMP stack, which bundles together a web server (apache, nginx), a DBMS (MySQL, PostgreSQL), and the PHP engine. A good good cross platform solution is XAMPP