Suppose you want to refresh a form or any content when a single row of CGridView is selected

how to achieve that ?

In your view file modify your cgridview like that

$this->widget('zii.widgets.grid.CGridView', array(
        'id' => 'my-items-grid',
        'dataProvider' => $model->search(),
        'selectableRows' => 1, //permit to select only one row by the time
        'selectionChanged' => 'updateABlock', //javascript function that will be called
        'filter' => $model,
        'columns' => array(
            'id',
             ...
             ...

Into the same view just add this (or using javascript register)

<script type="text/javascript">
    function updateABlock(grid_id) {

        var keyId = $.fn.yiiGridView.getSelection(grid_id);
        keyId  = keyId[0]; //above function returns an array with single item, so get the value of the first item
    
        $.ajax({
            url: '<?php echo $this->createUrl('PartUpdate'); ?>',
            data: {id: keyId},
            type: 'GET',
            success: function(data) {
                $('#part-block').html(data);
            }
        });
    }
</script>

In your controller add the appropriate action method

public function actionPartUpdate($id = null) {
        $model = MyModel::model()->findByPk($id);
        if ($model === null)
            throw new CHttpException(404, 'The requested page does not exist.');

        $this->renderPartial('_myModelview', array('model' => $model));
        Yii::app()->end();
}

view file _myModelview.php could be contains any code including $model data. Remember to includes you code between this

<div id='part-block'>
//your php-html code
</div>