How do I gain access to 'get_user_meta' function?

Hi everyone, I’m trying to create a simple plugin that access member data. I’m trying to use get_user_meta but nothing happens when I use this example:

<?php
$user_id = 9;
$key = ‘last_name’;
$single = true;
$user_last = get_user_meta( $user_id, $key, $single );
echo ‘<p>The ‘. $key . ‘ value for user id ‘ . $user_id . ‘ is: ‘ . $user_last . ‘</p>’;
?>

My site is live so I’m testing using my email like this:

function myFunction()
{

$user_id = 9;
$key = ‘last_name’;
$single = true;
$user_last = get_user_meta( $user_id, $key, $single );
echo ‘<p>The ‘. $key . ‘ value for user id ‘ . $user_id . ‘ is: ‘ . $user_last . ‘</p>’;

$to=”[email protected]”;
$subject=”Subject”;
$message=”Message : “.$user_last;
mail($to,$subject,$message);
}

add_action(‘wp_login’, ‘myFunction’);

Do I need some global variable to gain access to ‘get_user_meta’?

Thanks for any help.