http://developers.facebook.com/docs/authentication/

http://www.facebook.com/developers

appを登録して sample codeをクリックすると以下のように。

Follow the simple steps below to create a working skeleton for your Application.
Step 1: Download Facebook's PHP Library
Extract this archive into a directory on your hosting server where you can host and run PHP code:

$ curl -L http://github.com/facebook/php-sdk/tarball/master | tar xvz
$ mv facebook-php-sdk-* facebook-php-sdk
$ cp facebook-php-sdk/examples/example.php index.php
Step 2: Replace the IDs in index.php to have your own app information
It should look like this when you're done:

<?php
// Awesome Facebook Application
//
// Name: aucru
//

require_once 'facebook-php-sdk/src/facebook.php';

// Create our Application instance.
$facebook = new Facebook(array(
  'appId' => '',
  'secret' => '',
  'cookie' => true,
));
Step 3: Test Your Application
You're almost done!

We just need to know two more things. Edit settings for your application and enter:

The Canvas Callback URL - where your app is hosted.
The Canvas Page URL - the apps.facebook.com/yourapp URL for your application.

facebook-php-sdk/examples/example.php
を該当ドメインの下に fbtest.phpとして置きました。

require_once ‘facebook-php-sdk/src/facebook.php';
を置いてあるpathに変更。

アクセスすると

php-sdk

Login using OAuth 2.0 handled by the PHP SDK: Login with Facebook
PHP Session

Array
(
)
You are not Connected.

Login with Facebookのリンクをクリックしてログインすると

php-sdk

Logout
PHP Session

Array
(
    [fb_999999999999999_code] => 
    [fb_999999999999999_access_token] => 
    [fb_999999999999999_user_id] => 
)
You


Your User Object (/me)

Array
(
    [id] => 999999999999999
    [name] => 
    [first_name] => 
    [last_name] => 
    [link] => 
    [location] => Array
        (
            [id] => 
            [name] => Shinagawa-ku, Tokyo, Japan
        )

な感じでデータ取得できました。