Getting data from a table using a query

I’m starting with WordPress and I have a lot of problems and doubts.

I’m trying to display on a page data stored in a table of my database.

I have a table named Customers (id, name, surname, phone). Im adding code to the main page of the website:

[php]

$idCon = mysql_connect('localhost','user','password');

if(!$idCon){ echo "Error connecting database."; exit; }

mysql_select_db("database",$idCon); $query = "SELECT * FROM CUSTOMERS"; global $respuesta = $wpdb->get_results($query);

foreach( $respuesta as $row ) {

 echo $row->nombre; } 

$reg = mysql_fetch_row($res); mysql_close($idConn);

[/php]

But nothing is displayed in the page. Can you help me?

By the way, how can i debug code in wordpress ? That should help me a lot.

Thanks