The Site Overlay report opens a new window in your browser and loads your homepage. The homepage has stastistics hovering above each clickable link showing: % that click, % of revenue each link brings, % of transactions, % of goal value, and % that each link contributes to goals.

To set which statistic to show, click the down arrow in the top bar.
Hover over link statistic to get more information.
Hide Overlay - hides the statsitics and just shows the homepage with the Google Analytics bar at the top.
Close - hides statistics and Google Analytics top bar.