$a->config['facebook']['appid'] = 'xxxxxxxxxxx';
$a->config['facebook']['appsecret'] = 'xxxxxxxxxxxxxxx';
Replace with the settings Facebook gives you.
+ d. Navigate to Set Web->Site URL & Domain -> Website Settings. Set Site URL
+ to yoursubdomain.yourdomain.com. Set Site Domain to your yourdomain.com.
2. Enable the facebook plugin by including it in .htconfig.php - e.g.
$a->config['system']['addon'] = 'plugin1,plugin2,facebook';
3. Visit the Facebook Settings section of the "Settings->Plugin Settings" page.