The main area is meant for news, events and similar content: lots of change here, daily updates, with a quick glance you'll know what's going on in your company. Contents for this area are usually specifically edited because there is not much room.
The sidebar on the right is meant for the bulk of the information you want to make available. Access to older news and static contents, information from HR like job opportunities, image galleries, presentations from different departments, security information, your company vision, etc. Think of the sidebar as a two-tiered navigation menu through all the contents you want to be easily accessible from the boards. Pages you include in your sidebar can be from anywhere within your Confluence. You don't have to set up this information separately.
The footer at the bottom is meant for a handful of pages that contain information that are most important for users of your touch device: What's for lunch, where to find meeting rooms, a bus timetable, etc. Here too, you don't have to offer special pages if the contents you want to show already exist in your intranet.
Of course you don't have to stick to this plan - feel free to put your contents wherever they seem to be at the right place for your specific use case.