Google provide a free tool which allows you to track and monitor activity on your website called Google Analytics. The tool allows you to create reports and generate data relating to the amount and type of traffic that your website is receiving in order for you to make any required changes in an educated manner to improve the sites overall performance.
Google Analytics provides a mixture of pre-defined and custom report structures which are free to use. All of the analytics use real-time data, therefore the results are accurate. Alerts can be set up to advise you if and when the general dynamics of your website traffic change; for example if you launch a 20% sale at 5pm and there is a subsequent spike of traffic to your site this is an indication that the sale is a success as a marketing tool.
The Google Analytics tool is a means to gauging how visitors react to your site so that you can continuously improve it for them, and in the process improve your search engine result page ranking. It is the most powerful and best tool available for this kind of analysis, so it is a bonus that it is also free!