Having a working install of Ubuntu 13.04, proceed with the below;
1. Update and upgrade Ubuntu
$ sudo apt-get update
$ sudo apt-get upgrade
2. Install Nginx
$ sudo apt-get install nginx
$ sudo /etc/init.d/nginx start
Nginx should be working now. Try access the server from a browser.
3. Install PHP-FPM
PHP-FPM is a daemon process (with the init script /etc/init.d/php5-fpm) that
runs a FastCGI server on the socket /var/run/php5-fpm.sock.
$ sudo apt-get install php5-fpm
Now create the following PHP file in the document root /usr/share/nginx/www
$ vim /usr/share/nginx/www/info.php
// Enclosed in PHP tags of course
phpinfo();
Ps: See link 1 below for more detail & some other extra stuff you could do.