how to connect and insert data in wordpress database code example

Example: insert data to table in wordpress

if ( isset( $_POST['submit'] ) ){

         global $wpdb;
         $tablename = $wpdb->prefix.'post_job';

        $wpdb->insert( $tablename, array(
            'organizationname' => $_POST['organizationname'], 
            'post' => $_POST['post'],
            'publishfrom' => $_POST['publishfrom'], 
            'publishupto' => $_POST['publishupto'],
            'qualification1' => $_POST['qualification1'], 
            'qualification2' => $_POST['qualification2'], 
            'qualification3' => $_POST['qualification3'],
            'qualification4' => $_POST['qualification4'], 
            'experience1' => $_POST['experience1'], 
            'experience2' => $_POST['experience2'],
            'experience3' => $_POST['experience3'], 
            'training1' => $_POST['training1'], 
            'training2' => $_POST['training2'], 
            'training3' => $_POST['training3'],
            'training4' => $_POST['training4'], 
            'training5' => $_POST['training5'] ),
            array( '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s' ) 
        );
    }