$koneksi    = mysqli_connect($server,$id_user,$nama,$username,$password,$level);

$selected   = mysqli_select_db($koneksi, $database)or die("Couldn't open database $database");

<?php
$server = "localhost";
$id_user = "";
$nama   = "";
$username = "root";
$password = "";
$level  = "";
$database = "penjualan";

$koneksi    = mysqli_connect($server,$id_user,$nama,$username,$password,$level);
$selected   = mysqli_select_db($koneksi, $database)or die("Couldn't open database $database");
?>