First of all, Facebook doesn't allow other applications to authenticate to Facebook by using email and password.
Facebook has released a Facebook API which allows 1) your application to be registered in Facebook and 2) through your application, you can get a user Session Key (which is essentially your application authentication for a user's behalf).
FBRocket essentially wrapped the Facebook API to make Facebook RESTful function call easier in Java (for Android).
For full spec on the Facebook API, visit: http://wiki.developers.facebook.com/index.php/API
To know how Facebook Authenticate your application, http://wiki.developers.facebook.com/index.php/How_Facebook_Authenticates_Your_Application.
In short, create a Facebook Application, get a Facebook application ID
and application secret
(from Facebook) and you're good to go to getting all you want using the Facebook API.