Drupal Theme Blocks
All the preinstalled Drupal themes have the same built-in blocks described below. Also, you can create your own blocks and move them to any region you want. This can come in handy for posting images to the Right Sidebar, for example.
Standard built-in blocks appear in all of the preinstalled Drupal themes. You can see a few of them, where we’ve opened the Bartik theme’s Blocks administration overlay.
The default built-in blocks are
Navigation: The Navigation block contains the administrator links when you are logged in as administrator, and the My Account and Log Out links for logged-in users. It also displays the username.
User Login: This block contains the User Login form. It's only visible when a visitor to the site has not yet logged in; if a visitor is logged in, the block is not visible. This block also contains Create New Account and Request New Password links.
Powered by Drupal: This little block contains a link to Drupal.org when you click it.
System Help: This block contains a search text box that provides users with a means for tracking down tips on using Drupal.
Main Page Content: As its name suggests, this block displays the main or central content of a given page.
Search Form: The search form block is for — you guessed it — entering site search queries for site-specific content.
In most themes, the following blocks are disabled by default:
Active Forum Topics: This block becomes available only if the Forum module is enabled.
Management: This block contains all of the links already available via the Drupal Management menu.
Most Recent Poll: This block is designed to inform site visitors of the most recent poll posted on your site. This block becomes available only if the Poll module is enabled.
Main Menu: When enabled, this block offers users another access point to the links usually located at the top of your site.
New Forum Topic: When enabled, this block will alert users to new forum topics. This block becomes available only if the Forum module is enabled.
Recent Blog Posts: This block displays recent user blog posts on your site. This block becomes available only if the Blog module is enabled.
Recent Comments: This block provides site visitors with an overview of recent comments posted to your site.
Recent Content: This block provides site visitors with an overview of content posted to your site.
Shortcuts: This block lists links to internal and external links, allowing your visitors to navigate easily to areas of interest on your site and elsewhere on the Internet.
Syndicate: This block adds a logo and a link to the XML version of your site pages, which allows users to grab and use the syndicated content from your site.
User Menu: This displays a number of options for registered site users, offering items like account access and if enabled, the capability to manage their account settings.
Who's New: This displays usernames and links to profiles of the newest registered users of the site.
Who's Online: Shows a summary of how many people are currently using the site, divided into registered users and people who aren't logged in. It also shows a list of the registered users and links to their profiles.