Google Analytics is the most popular free tool for measuring the success of your marketing efforts.
If you use Google Analytics correctly it can be a very powerful tool for your business. With it, you can view the volume of your website traffic, track where your website visitors are coming from and where they are going, and learn how and why people are visiting your website over any given period of time.
Understanding the demographics, behaviors and interests of your website visitors improves your online marketing.
This infographic paints a clear picture of how to use Google Analytics data to improve your (online) marketing.
Source: Quick Sprout