All of the content that is displayed on a Quickstart page is organized into regions. The image below shows all of the regions and their names.
Most Quickstart content is already set up in the appropriate region and you will not typically need to do anything other than add your content and organize your menus.
However, some content, such as blocks, search bars, resource menus and call to action buttons, require a basic understanding of regions. Think of a region as an area where your content will go.
The most basic use of regions is to place content, such as a group of events in a sidebar. Note that out of the box, content is already organized into blocks and regions! Even sidebar navigation has already been configured out of the box. All you have to do is add the content.
Under most circumstances, only advanced Quickstart users and site builders will need to know the regions and modify the content within them. That is managed in Admin > Structure > Blocks.