With WP Client Reports Pro, you can add a new section to your report that gives you and your client informative base level metrics for your site during a set amount of time.
Google Analytics is the de facto standard for measuring web traffic for many websites. It is free and allows advanced reporting in a plethora of ways. You will need a Google user account in order to use it.
Once you have a Google Analytics account set up, you will need to install their tracking code so that as visitors browse your website, the information will be sent to Google Analytics. This tracking code is NOT added by the plugin. There is a nice tutorial on the various ways to accomplish this here.
Related documents: Learn how to set up the integration with Google Analytics within the plugin with this tutorial.