求解释 [ 新手入门 ]

public function actionIndex()
{
        
    if(isset($_GET['ad']))
    {
        $ad = $_GET['ad'];
        ResourceBehavior::counter($ad);
    }
    if(isset($_GET['khd']))
    {
        $ad = $_GET['khd'];
        ResourceBehavior::counter($ad);
    }
}

这是什么意思？