Google Analytics is a platform owned by Google where you can track your website traffic, where your visitors are coming from and a number of other interest and behaviors while they are interacting with your website.
With this information you will be able to recognize patterns and see how you can target the people who visit your website. This information will also give you the key words that they used to get to your website. This in turn can be used if you are looking to increase leads and sales when using Google AdWords to purchase ranking on the first page of Google when someone is looking for your product or service.
For small to medium sized businesses the free version of Google Analytics is a great start to focus on who is coming to your website and come up with a strategy to keep them coming back!