What is Facebook?

Facebook is a open social network. It is used by millions of people around the world. It is mainly used for sharing information. When you register an account at facebook, you will become a member of this network. And then, you can connect with other people in Facebook. Facebook is more and more becoming popular today. But some countries restrict people go to this website because they are afraid of people getting bad info from unknown source. Is this happening in our country, Vietnam?