There are many sites that you can not access in China, which include Facebook, Youtube, Twitter, and etc.

Chinese government uses IP blocking, DNS hijacking, and keyword intrusion detect system to censor the internet.

You can install a software called 'Freegate' to surf the internet freely in China without your IP address being traced.

If you don't not want to download any software to your computer, you can  establish encrypted VPN connection to unblock these sites via  sites like - www.gfwvpn.com/