1. Download 'ODude Facebook Login Module' and install it as you do for other modules.
2. After it is installed, go to the Module manager and click mod_odude_facebook.
3. To option Facebook Application ID, API key & Application Secret Facebook Applicatoin at Facebook.com

• First you need to log in to the Facebook Developer application:Go to the Facebook Developer App
  After following the link, click “Allow” to let the Developer application access your profile.
• Begin setting up a new application. Go to the Developer application and click “Set Up New Application”. Give your application a name, check to accept the Terms of Service, then click Submit. You'll see some basic information about your application, including:
• Application ID : ID of your facebook application.
  
• Your API key: this key identifies your application to Facebook. You pass it with all your API calls.
• Your application secret: Facebook uses this key to authenticate the requests you make. As you can tell by its name, you should never share this key with anyone.
• Set Convas Callback URL to your website URL to where you wish to open a page after login.
• Set Connect URL to your base domain name.
  
• Get Application ID, API Key & Application Secret and copy it into the ODude Facebook Module setting page.
• Carefully set the parameters for "Profile Link" &"Profile Photo".
  

These are the screen shots used in our demo site Joomla 1.5.

Joomla 1.6 users need to install extra Authentication Plugin included in package. You have to enable it else only Facebook will login but your site login form will remain as it is.