How to Tell if Click Came from Google Search

I'd like to know if there is a way to detec开发者_运维问答t whether the user has entered the website from an Organic Link from Google on certain key words?

What I am trying to do is provide additional information to appear to those who found my site via Google?

Thanks!

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Use Google Analytics

Sign up for an account and just add a small snippet of Javascript to your site. It's really easy to set up and track links from google and even the exact search terms used!