Installing Google Analytics is extremely simple.
1- Create a Google account if you don’t already have one.
2-Visit the Google Analytics website, click the Sign Up Now button, and follow the easy sign up process
3-Copy paste the code you are given, just above the closing body tag on all of your webpages (meaning your template or master page if applicable), then click the Check Status button on your Analytics interface, so Google can verify that your site is running the Analytics script.
And you’re done installing Google Analytics. Once you’ve verified that your code is up and running, Google Analytics will begin to do its magic. Give it a few hours for your metrics to start showing up.
New Tracking Code (ga.js) vs Legacy Tracking Code (urchin.js):
You are given the option of choosing the old Urchin legacy tracking code, or Google’s own newer version. At this point in time there’s no real reason to choose the old version (there were some bugs with it at first). The Urchin version only exists because it was Urchin that actually developed this tool, which Google purchased from them. If you choose the Urchin legacy code, you won’t get any of the newer features, as Google no longer supports it.