<?php
$servername="localhost";
$username="root";
$password="";
$dbname="test";

$db=mysqli_connect($servername,$username,$password,$dbname)or die(mysqli_error);

if(isset($_POST['autorization'])){
$username=trim($_POST['username']);
$password=trim($_POST['password']);
$username=mysqli_real_escape_string($_POST['username']);
$password=mysqli_real_escape_string($_POST['password']);

mysqli_query("SET NAMES'utf8'");
mysqli_query("INSERT INTO `mydb`(`username`,`password`) VALUES('$username','$password')");

$reslult=mysqli_query();
if($reslult== true){
    echo "message send";
}
 }
?>

<form id="form" class="form" method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">

<input type="text" name="username" placeholder="username"required/>
<input type="text" name="password" placeholder="Password"   required/>
<button type="submit"  name="autorization">Log-In</button>
</form>
<?php echo $result;?>