How work with Facebook Api in PHP?

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PHP

Apache

Facebook-API

Hello!
I got task in my university.
I have to create IFrame in facebook, check who is logged in facebook, read data and save in DB.
I'm newbie in PHP, I have never used facebook api and php.

1.When I start create account, needs to filling some fields interesting just 2:
App Domain: (What should I write here if I don't have domain? currently I have Denwer and using localhost:81)
App on Facebook: (What must I fill here in next 2 fields: Canvas and Secure canvas?)

2.I guessed to create button, when I click execute function, where:

$facebook = new Facebook(array('appId' => '2222....', 'secret' => '4444..'));
$user = $facebook->getUser();

I guess getUser gives data about my profile that logged now. If yes, I don't know how get data from this variable and save to DB.

Please help me.Thanks a lot

PS Also interesting, how can I get data about user if i have just eMail?