Changing Drupal Block Visibility Settings

By Lynn Beighley and Seamus Bellamy from Drupal For Dummies, 2nd Edition

When you create a custom block in Drupal, there are visibility settings at the bottom of the Add Block form. These settings can also be applied to the pre-built blocks. To see them, click the Configure link next to a block. The block visibility settings appear.

The visibility sections are:

Pages: This first option allows you to display your block on specific pages of your site. It requires you to enter the path to the pages on which you do or do not want the content to appear.

Before you can enter paths in here, you need more pages on your site.
Content Types: This option allows you to display your block on pages that display information of a certain type: Article, Basic Page, Blog Entry, Forum Topic, or Poll.
Roles: If you want to allow only registered users to see your block, this is where you control that. Leave everything deselected if you want both signed-in and guest users to see your block.
Users: These settings control whether registered users can choose to hide a block from view when they visit pages on your site. The first option gives them no control. The second lets them hide the block, but it is visible at first. The third lets them hide the block but lets them show it if they wish.

If you let them control the visibility, a check box with the block name will appear on their My Account→Edit page.