This function is really easy to access. On the results page of Google click on on the top.

Wonder Wheel - Google

The Wonder Wheel is a graphic way to search content by linking a topic to different sub-topic (e.g.: football to football training to NFL training).

It is a useful tool when you don’t know the best keyword for a specific subject. Just enter a generic keyword, click on the most relevant suggested link and Google will try to guide you to the right keyword.

This tool is not really an innovation, a few years back Microsoft devolved Tafiti with the same principle, with the exception that Tafiti uses the ‘new’ Microsoft technologies (Silverlight).

Tafiti - Microsoft

At the end of the day, I am not sure that a lot of people are going to use this option but it does explain a little how Google is working at the moment.