Google Analytics is a free web analytics service that provides statistics about visitors to websites. It was originally called Urchin and was acquired by Google in 2005. It allows users to track key metrics like number of visitors, traffic sources, and popular pages. While it provides sufficient analytics for most sites, it has limitations like only tracking visitors and not crawlers. Setting it up requires adding JavaScript tracking code to websites and connecting it to a Google account. Analytics can then be used to generate reports and gain insights to improve sites, especially important metrics for e-commerce sites like best selling products.