Proxy auto-config using .Net c#

Question

I am working on a project, Proxy auto-config using .Net c# . One of the requirements of the project is to detect the proxy,website whose who are accessing from the system and check whether that site is accessible for this ip or not, this is stored in the server according with the ip as file , this is the requirement .
Now i haven't worked with proxy before and hence i am a bit baffled. After hours of searching google, msdn etc, i have come across the following article http://www.codeproject.com/Articles/12168/Using-PAC-files-proxy
Now i am totally confused how to do this? Can someone please help me with an easier implementation or guide me please?
Sorry once again if i sound silly, but i haven't worked with .Net proxies and hence I am struggling.
Thanks in advance for your help.