On a standard Drupal installation, you need to run Cron Jobs (or tasks as they are called sometimes). Drupal will actually give you an status error if you don't run a cron job after you install Drupal.
Cron is driven by a configuration file that specifies Unix to run certain commands on periodically on a given schedule. This is how Drupal knows when to publish an article at a certain time and how it indexes the site for it's built in search engine. Without running Cron, Drupal would never do these items.