The standard GW Drupal layout consists of three columns:
A left sidebar for navigation and/or supportive elements
A center column for the main content of the page
And a right sidebar for additional supportive elements
Adding supportive elements, such as Promotions or List Sidebars, is a quick and easy process. On your subpages, there are dedicated "Right Sidebar Content" and "Left Sidebar Content" fields on the New Draft admin page. You just need to type in the name of the item you want to feature and then click on the matching result.
And for the GW Drupal Classic theme homepage, it's as simple as assigning the item you want to feature a Site Placement value of "Home".