Connecting to a database

<?php
$server = 'localhost';
$username = 'root';
$password = '';
$db = 'TNW';
$conn = mysqli_connect($server, $username, $password, $db);
if($conn){
echo 'Successfully connected to a database -' .$db. '.';
}else{
echo 'Connecting to a database Error.';
}
?>