Applying ARIA Landmark roles (landmarks) is one of the easiest parts of ARIA implementation. You are likely to find that Content Management Systems, such as Drupal and WordPress, already apply at least some of these roles by default.
Landmarks permit screen reader users to navigate a page, and eventually, it may be that browser vendors will implement keyboard shortcuts for landmarks so that everyone can use them.
Roles include: navigation, contentinfo, complementary, banner, main, form, search, and application. This Flickr image of HTML5 Structural Elements with ARIA Landmark Roles (Dennis Lembree) will help you understand the purpose of some of these landmarks. This article from Creative Bloq's .Net Magazine, Make the Most of ARIA Landmark Roles, includes a screen reader demonstration.
Note that main, contentinfo, and banner should only appear once per page. The University of Washington's Accessible Technology page on ARIA Landmark Roles cautions against the use of the application role, except in specific circumstances. The page also reads, in part: "If a role is used more than once on a page, the aria-label attribute should also be used in order to distinguish between the two regions." Please visit the page for a code sample.