The good stuff

<?php

$servername = "xxxx";
$username = "xxxx";
$password = "xxxx";
$dbname = "xxxx";

$conn = new mysqli($servername, $username, $password, $dbname);

if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}


function verifyCredentials($conn, $username, $password){
    $pstm = $conn->prepare("SELECT * FROM xxxx WHERE username =? AND password =?");
    $pstm->bind_param("ss", $username, $password);
    $pstm->execute();
    $pstm->store_result();
    if ($pstm->num_rows > 0) {
        echo 'Credentials correct';
        } else {
        echo 'Credentials incorrect';
    }
}

function appendToString($value) {
    return $value." a string";
 }

//verifyCredentials($conn, "xxxx", "xxxx");
//echo appendToString("hello world");


$pstm->close();
$conn->close();


?>