Login page in PHP with Source code

<?php
$dbname="databasename";
$con=mysqli_connect('localhost','root','databasename');
if($con->connect_error)
{
             die("error");
}
$u=$_POST["username"];
$p=$_POST["password"];
$finalResult = mysqli_query($con,"SELECT * FROM register WHERE username='$u' and password ='$p'");
$confirm = mysqli_fetch_array($finalResult);
if(is_array($confirm))
{
 session_start();
 $_SESSION['username']=$u;
 header("location:usersection.php");
}
else
{
echo "<script>alert('Wrong Username or Password');window.location='home.php';</script>";
}
?>