The easiest way is using a web proxy. Visit http://microxy.com and enter the website you want to browse in the surf bar and press now go, you will get what you want.
Proxy servers are use for secure and anonymous browsing experience. Some servers are private/secured and stronger than others. So you can pay for unique strong private ones using companies like iprental.com
the "why" response could be very long... so I'm going to answer just the first one. Using a proxy server is very easy, firs find a proxy IP and port, then go to your firefox preferences, under network, advanced, and just write the IP address and port, save and done! All your web requests are being through the proxy that you choose.
GoProxy is right, the answer could be very long. So, here's my short version ... One reason to use proxies is to hide/protect your online identity. If you're doing something in the blackhat realm, you probably want to hide your true location (IP address). If you have been or could be banned from a site, you probably want to hide your true location (IP address). If you're in a country that does not allow something like online gambling, and you want to visit a gambling site, you probably want to hide your IP. Another reason for proxies is it you're using a piece of software that is multi-threaded, that is, it is repeating an activity, you probably want to hide your IP. Otherwise sites would know its you, and block you from visiting their website. Hope this helps!
I recommend to use Hotspot shield, which is just like proxy only software, so it`s faster and easier to use. Also we use proxy to hide our real Ip address