This panel allows you to drag and drop columns from the table onto it.
 
If you click on a column header, hold down the left mouse key and drag the column header to this panel, then the table will be rearranged and grouped by that column. This can be done a number of times allowing you to drill into the specific information you are seeking.
 
It is best for you to experiment with this very powerful feature.
 
To undo or change your view, right click anywhere in the panel and select the option you wish.