From Facebook Developer Wiki

Facebook Connect sites use the JavaScript Client Library to access Facebook Platform via JavaScript. Here are some tips to help you get started.

• To use the Facebook Platform REST API with Connect, use the FB.ApiClient class.
  Note: Not all API methods are supported. Which methods you can use depend on whether or not you're using a session secret (which you get when you create an application with the Facebook Developer application -- see Trying Out Facebook Connect for details). If you're not using an application secret, you can't use admin methods or methods that set data on a profile (like profile.setFBML).

• To log users in, use FB.Connect.requireSession.
  Note: If you're having your users log in via fb:login-button, Facebook verifies the session for you, so you don't need to call this function. Read more about logging in users.

• To invite users to connect with their friends, call FB.Connect.inviteConnectUsers.

• To determine the user's Facebook Connect state (whether the user has authorized your site, and if so, whether the user is logged in or has connected accounts), use FB.ConnectState -- which describes the user's Connect state (used in connect.getStatus).

• For XFBML, you can manage XFBML elements with FB.XFBML.Host.

• To create XFBML elements without using XFBML tags, use FB.XFBML.Host.AddElement and FB.XFBML.Host.AddElements.
  Other elements in the XFBML namespace are similar to the XFBML tags.