By default, the Graphene theme provides 3 widget areas: the right sidebar, left sidebar, and just above the footer. However, as you’ll see, it also provides options that virtually allow you to place unlimited number of widget areas in your site.
Alternate front page widget area
Apart from the default widget areas, the theme also includes a feature that allows you to have alternate (or separate) widget areas for the front page. What this means is that you can have a set of different widgets being displayed only on the front page, and a different set of widgets for all other pages.
Action hooks widget areas
This is the feature that allows you to virtually place unlimited widget areas at every nook and cranny of the theme. Basically, this option will let you create a new widget area for every action hook embedded in the theme.
It’s probably better explained by the introduction post of this feature, or see the video tutorial below by Josh Lobe.