The following method will get you started fast on Ubuntu 12.04:

Install the dependences:

sudo apt-get install php5-common php5-cli php5-fpm

Install nginx:

sudo apt-get install nginx

Start nginx:

sudo service nginx start

Test that it's working (should see "Welcome to nginx!")

sudo service nginx stop

In your nginx site configuration (/etc/nginx/sites-available/default), modify the line in the server {} section

index index.html index.htm to index index.php index.html index.htm.

Uncomment the lines in the server {} section starting with

listen for ipv4 / ipv6 both.

Scroll down to where it says location ~ .php { and uncomment lines so it looks like this:

location ~ .php$ {

  fastcgi_split_path_info ^(.+.php)(/.+)$;

  fastcgi_pass 127.0.0.1:9000;

  fastcgi_index index.php;

  include fastcgi_params;

}

sudo service php5-fpm restart
sudo service nginx restart

Your default web root is located at /usr/share/nginx/www (per the config file). (See root /usr/share/nginx/www;

(Note: For Ubuntu 12.10 or newer, you will need to replace the fastcgi_pass 127.0.0.1:9000; line with this to make it work: fastcgi_pass unix:/var/run/php5-fpm.sock;)