Install the module in Joomla!
Go to the administrator (yourdomain.com/administrator) and log in.
Go to 'extentions' - 'extensions manager'.
Then upload & install the zip-file of the module Joomla Login with Facebook Connect.
The module is installed.
Go to 'extentions' - 'module manager'.
Find the module 'Login with Facebook Connect' and click on it.
Now you can choose a position (where to put the module in the template), publish it and choose in the tab 'Menu Assignment' on which pages you want to publish the module.
You must get the Facebook credentials to setup your module completely:
Go to http://www.facebook.com/developers/createapp.php and follow the wizard.
On the tab 'website' you need to fill-in the field 'Site-URL' with the URL/address of your joomla installation and save it.
You'll need to copy the Application ID and the Application Api Secret.
Copy-paste these values into Joomla in the window where you can edit the module. On the right you'll find a few fields, fill in the Application ID (needed!) and Application API Secret (needed!)
Save to the module and you are ready to use it on your website!