How does Facebook Connect work?

I want to know in detail how Facebook Connect works. For example, if I install Facebook Connect on my site, how does that help me? What information about my users will I be able to see/access from Connect? What information, site activity, user information will Facebook get access to from users on my site that login with Connect? For the activities/information that users provide on my site, who owns that data/information? Me or Facebook? thx in advance for the help!