what plugin to use? classified ads that connect to facebook to post ads

Hi,

I checked this website (http://www.oodle.com/) and see one nice feature. When the user want to post the ads, the user need to connect it with the facebook. How do i do that? I want to create a classifield ads website for free but they need to connect to FB when to post it. But that would mean my website must be able to have membership plugin too? any idea on what do use for that website?