We'r using https://github.com/ashwinks/PHP-LinkedIn-SDK. All documentation is there. I have added example for posting content on user's wall.
Open up index.php
Init class with your app id and app secret
$li = new LinkedIn(
array(
'api_key' => 'YOUR_APP_KEY',
'api_secret' => 'YOUR_APP_SECRET',
'callback_url' => 'CALLBACK_URL_REGISTERED_WITH_APP'
)
);
Make sure that your callback url matches your callback url registered with app. In our case, we are handling callback in same file. Thats pretty much it! Let me know if any queries.