$user = 'root';
$pass ='';
try {
    $pdo = new PDO('mysql:host=localhost;dbname=tests', $user, $pass);
} catch (PDOException $e) {
    print "Erreur !: " . $e->getMessage() . "<br/>";
    die();
}

//Recieving datas from POST
$firstName = $_POST['firstName'];
$lastName = $_POST['lastName'];

//Creating username - First letter of first name followed by last name +
current timestamp for joinDate + email
$firstLetter = $firstName[0];
$username = $firstLetter.$lastName;
$email = $username . '@gmail.ch';
$joinDate = time();

//Query for inserting users data into database
$query = $pdo->prepare("INSERT INTO users (lastName, firstName, username,
email, joinDate) VALUES (:lastName, :firstName, :username, :email,
:joinDate)");
$query->execute(array(
    ':lastName' => $lastName,
    ':firstName' => $firstName,
    ':username' => $username,
    ':email' => $email,
    ':joinDate' => $joinDate
));
var_dump($query);