The database module is included with the Kohana 3.0 install, but needs to be enabled before you can use it. To enable, open your
application/bootstrap.php file and modify the call to Kohana::modules by including the database module like so:
Kohana::modules(array( ... 'database' => MODPATH.'database', ... ));
Next, you will then need to configure the database module to connect to your database.