The pages below give help for the modules that come with Drupal. When you install Drupal, these modules are automatically installed. To make use of a module, first make sure it's enabled at administer >> site building >> modules. (Some modules automatically are.) Then set the right permissions for it at administer >> user management >> access control.
You can further extend the features of Drupal by using "contributed modules." A list of help pages for contributed modules is available at the contributed modules page.