Drupal is not a page management system but a content management system. That may seem obvious, but it's actually an important distinction; Drupal doesn't think in terms of pages but in pieces of content. Not every page that will be displayed is a piece of content, and not every piece of content will have a page.
Figure 1, Drupal StackTo understand how to build pages in Drupal, it's important to understand the Drupal Stack; that is, the order in which a Drupal architect will approach a build-out. There are actually four separate and distinct concepts at work: Content, Data slices, Layout, and Display.