If you are looking at improving the usability of your website, one of the first steps is to see how your users are trying to use the site. You can start with your website statistics to get an idea of the "top ten" pages they use. You might even have additional analytics that reveal how long a user remains on the site, and where they are from.
But I can speak from experience that seeing where users are clicking provides a very compelling case. The Useful Usability blog lists 24 website usability testing tools that you may find interesting. I've mentioned Ethn.io in another post. At work, we have used Crazy Egg. You may also be interested in the open source software tool ClickHeat.
These tools help to generate a "heat map" of your users' navigation habits. Where are they clicking? How much of the screen can they see?
As always, this is just one tool that you can use to analyze the current usability of your website. Don't forget to start with a user-focused design with personas and scenarios, and to do a full usability analysis.