Hi, i am in the process of finishing off my sign up form on my site.

I like most people here, would not use a social network to sign up to any website... i'd rather use an email address, HOWEVER, some people do use them.

So, i am just about to start integrating the Facebook and Twitter Sign Up APIs into my site, however i have a few questions.

1 - how do these work, what is the general process involved (what happens when they choose once of these methods)
2 - once a user signs up with one of the apis, is their info (such as first name, last name, email address) pulled from the Facebook or Twitter database, then saved in my database
3 - if i need to display some of the users details on my site (such as first name), where will the site be pulling the details from, my database or the social network database

Thanks in advance to any help you can give on any of the above questions