Drupal is a free and open source content management that supports websites ranging from personal blogs, corporate brochures and large community-driven websites. It has a flexible platform that allows users with variety options to include changing how web site looks, how users interact with it, and the kinds of information to display.
One of the basic configuration options in the Drupal system is the Block functionality. Blocks are those boxes that you see in the sidebars of the Drupal website. The blocks that you see are mostly generated on the fly by various Drupal modules. On the fly means that these blocks were created when needed. Other than those, users can create their own blocks. A block is a snippet of code that gets called from your template files. All the templates that make up a page are laid out in the master template. The location of the blocks on your web page will depend both on the theme enabled and on administrative block settings. The control of the block settings are perform under the block administration screen, which can be reached through clicking the administer >>blocks. On this screen, you will be able to enable each block and locate where the block should be placed on the page and which pages the block should appear on.
Drupal’s block custom visibility settings should permit the block to be displayed for a given user. You can set a particular block setting to either appear always and display by default unless individual user preferences has chose to disabled it. The Drupal block system has the feature of allowing individual users to select or disable optional blocks from their "my account" page.