Facebook is a free social networking website that allows users to create profiles, connect with friends, join groups, post photos and updates, and use applications. It was founded in 2004 by Mark Zuckerberg and has grown to over 200 million users worldwide. Users can customize their privacy settings and limit what they share publicly versus privately with friends. While the site aims to help people connect, it also warns that users may encounter online harassment, disturbing content, and even addiction to the social platform.