The Gem Theme comes with a broad range of layout options.
The blue widget positions allow to choose a widget layout which defines the widget alignment and proportions: parallel, stacked, first doubled, last doubled and center doubled. You can easily add your own widget layouts.
The two available sidebars, highlighted in red, can be switched to the left or right side and their widths can easily be set in the theme administration.
Scheme above is also available at Appearance->Widgets, top of the page click "Show Widgets layout scheme".
Home Page Components
Gem is a widgets focused theme. Each page can includes a system output(page content, posts) and widgets that are located in different positions.
The following are the Homepage components. It consists of widgets that are in different positions. Manage widgets you can in Appearance->Widgets. Assign widgets to specific pages with Gem->Widgets.
This scheme will help you to create and edit pages and adjust them to fit your requirements. Also read widgets setting.