Can anyone give me idea that how google record conversion after a user clicking a particular ads.

using cookies and IP tracing .

Using cookies Google provides personalized and most intelligent data to Gogglers when they search on Google.

search about " Google privacy policies and security" .. Then you will get info about privacy of Google. This is a big info otherwise i can write here about new privacies of Google"going to implement from march,2012

Thanks for the information Salinajohnson. Its helped me a lot.

You can use google analytics for this purpose, which can track all the behaviours of your website visitors, like the time they stay on each page, users oprating system, his location, his demographics, Your CONVERSIONS and many others....
Give it a try, its very helpful

It is really very complicated thing to tell, I would say.

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