<?php
$username = $_POST['username'];
$password = $_POST['password'];

$userdata = array($username, $password);
$encode = json_encode($userdata);

$query = mysql_query("insert your mysql query");
if(query) {
	echo "success";
} else {
	echo "fail";
}

?>

//HTML
<input type="text" name="username" id="username">
<input type="text" name="password" id="password">
<button id="button">submit</button>

//JS
$('#button').click(function() {
	var username = $('#username').val();
	var password = $('#password').val();
	$.ajax({
		type: "POST",
		url: "gantisesuailokasifilephp",
		data: "username=" + username + "&password=" + password,
		cache: false,
		success: function(response) {
			alert(response)
		}
	});
});