To enablel gii in yii we should edit ‘modules’ after entering yii\protected\config\main.php . Snippet are showing belows:

'modules'=>array(
		'gii'=>array(
			'class'=>'system.gii.GiiModule',
			'password'=>’type password’,
			'ipFilters'=>array('127.0.0.1','::1'),
		),

url manager remains in yii\protected\config\main.php. We can enable after un commenting ‘urlManager’ and the codes will show like:
'urlManager'=>array(
			'urlFormat'=>'path',
			'showScriptName'=>false,
			'rules'=>array(
				'<controller:\w+>/<id:\d+>'=>'<controller>/view',
				'<controller:\w+>/<action:\w+>/<id:\d+>'=>'<controller>/<action>',
				'<controller:\w+>/<action:\w+>'=>'<controller>/<action>',
			),
		),

: A controller is an instance of CController or of a class that extends CController. It is created by the application object when the user requests it.

controller convention:  The ControllerID in CamelCase suffixed with ‘Controller’ ex. SiteController, where Site is the ControllerID.

Method convention:  camelCase with first letter lowercase like getProperty(),actionCreate().Ex:
public function actionCreate()
            { 
block of statement
             }

Yii applications are built upon components which are objects written to a specification. A component is an instance of CComponent or its derived class. Using a component mainly involves accessing its properties and raising/handling its events.  
Example:  CDbConnection this component provides a database connection.
[page#25(pdf),  http://www.yiiframework.com/doc/guide/1.1/en/basics.component]

Yii has several types of database support those are 
 a. SQL via DAO
 b. query builder
 c. Active Record