What does actually a proxy web site do?

Proxy Web Sites are most of the times used to access blocked websites at school,work,colleges,universities and libraries. Proxy Sites also provide you with anonymity and some other extra security features. Using a Proxy Web Sites, helps you by masking your real IP address with the IP of the provider,in other words you don't let others to see your real IP as you will be using the Web Proxy's IP. That's not all ,by using a proxy site you will be able to access several social networking sites and not to mention that you will be able to watch online videos on YouTube or DailyMotion as most of the Proxy Sites support javascript and videos!