The Facebook connect enable you to login a user into your website using his Facebook account, and the ability to request and display his Facebook information into your application or website.
Once a user has granted your application the permission to interact with his Facebook account, you can:
- Store the Facebook token into your database to authenticate the user in the future
The possibilities are large and depends on what you need to implement in your application.
Your can read the Facebook API documentation to learn more about it.