Block Instances provides visbiliy controls for all existent blocks. If a module provides a block (like views blocks or the user login) you will be able to display it by creating a block instance.
Manage block instances
To administer the existent block instances, you should go to Administer -> Site Building -> Block instances.
Here you will see a list of created block instances. A block instance can live in the database, or be loaded directly from a module.
To create a new block instance, click on the Add tab at the top of the screen. To edit an existent block instance, click on the Configure link of the proper instance.
Sort block instances
The enabled block instances will render a block in a specific region of the theme. The position in wich they are displayed can be managed draging and dropping a block instance via an specific interface that can accessed trough the Sort tab at the top of the screen.
Creating and editing instances
To know how to create or edit a block instance, click here.