In China many websites are blocked which includes some of the major sites such as Facebook, Youtube, Twitter, and a number of Google sites. Apparently there were search engines in China that censored certain words. The government censors/censored such topics as the environment and topics such as Tibet and Xinjiang.
After conversations with a young Chinese man today I was told that the government blocks these sites so that the people cannot get information about other countries or their own - China.
Most uneducated Chinese people don't care much about the censorship. I guess it's hard to care about what you don't know. However, those who are more educated tend to know how they can get around the firewall by using a proxy or a VPN.
Things are changing though and he thought that in maybe 10 years there won't be any more censorship in China. When I lived in Shanghai I didn't find it to be a big deal. I had a VPN and could access pretty much everything. I did think that the internet was pretty slow though, at least it was where I was living.
For more information on VPNs and proxies I would do a search on Shanghai Expat.