can any one explain about the system by which google detects that the person which is clicking on the google adds is the admin of the site or some visitor....
Simple... Admin logs in to their AdSense account. Google records IP (and browser, OS, geolocation and other stuff). Admin clicks his own ads, Google matches it against list of login IPs, BANG! Not saying that's what they do but technically, it's dead simple.
What T0PS30 said.. It's very easy to detect and they have many ways. I wouldn't even play around with such things if you are even half serious about making any money with AdSense. Never, ever, ever, ever, ever, ever, ever click your own ads or have friends/family click on them nor entice anyone to click on them beyond the means laid out in the TOS.
They can detect any any of the methods of clicking.. thats why G!! is known as BIG DADDY... i personally tried clicking from differnt IP's Cmputers ( but they emailed me, i wasnt banned).. this was almost like a 1 year ago So beware G is da SMARTEST
Foruall, it sounds to me like you want to cheat and steal from advertisers. I'd strongly advise you against it. Just get the idea out of your head, it's not right.