They are generally used for evergreen content that doesn’t change very often, like a “About Us” or “Contact Us” page. Unlike posts, they generally don’t support taxonomies (like categories and tags). Comments are deactivated as default on pages, but they can be activated by checking the “Allow comments” checkbox in the “Discussion” meta box while editing a page.
Pages can be arranged in hierarchies to create page structures. An “About Us” page could for instance have the sub pages “Contact Us” and “Our Employees”. Different themes display page hierarchies differently, but they are commonly included in breadcrumbs (in the form “Home → Parent Page → Sub Page”) and menus. Pages can use Page Templates to adjust their functionality and appearance.