Why is this SQL not working

[Gang67]

It isn't sending the data to my database nor showing error messages

<?php
session_start();
//connect to database
$db=mysqli_connect("localhost","root","{DB PASSWORD}","rppp");
if(isset($_POST['register_btn']))
{
    $username=mysql_real_escape_string($_POST['username']);
    $email=mysql_real_escape_string($_POST['email']);
    $password=mysql_real_escape_string($_POST['password']);
    $password2=mysql_real_escape_string($_POST['password2']);
     if($password==$password2)
     {           //Create User
            $password=md5($password); //hash password before storing for security purposes
            $sql="INSERT INTO users(username,email,password) VALUES('$username','$email','$password')";
            mysqli_query($db,$sql);
            $_SESSION['message']="You are now logged in";
            $_SESSION['username']=$username;
            header("location:home.php");  //redirect home page
    }
    else
    {
      $_SESSION['errormessage']="The two password do not match";  
     }
}
?>

<div class="content">
<form method="post">
    <input type="text" name="username" id="username" class="form" placeholder="Username"> <br /><br />
        <input type="text" name="email" id="email" class="form" placeholder="Email"> <br /><br />
            <input type="password" name="password" id="password" class="form" placeholder="Password"> <br /><br />
        <input type="password" name="password2" id="password2" class="form" placeholder="Verify Password"> <br /><br />
            <input type="submit" name="register_btn" id="register_btn" class="submit">
         </form>

 

[Menkz]

What CMS are you using?

 

[Gang67]

What CMS are you using?

Trying to make my own

 

[Mikee]

Trying to make my own

I don't have any help to give you only a comment of well done. I must say that I am impressed. You've gone from a noob asking simple questions (which we all have asked from time to time) to pushing yourself to teach yourself to code and make your own cms, in what I think is a relatively short amount of time. Well done, I have a high level of respect for you. Keep going, never give up, and I'm excited to see your work in the future.

 

[Gang67]

I don't have any help to give you only a comment of well done. I must say that I am impressed. You've gone from a noob asking simple questions (which we all have asked from time to time) to pushing yourself to teach yourself to code and make your own cms, in what I think is a relatively short amount of time. Well done, I have a high level of respect for you. Keep going, never give up, and I'm excited to see your work in the future.

Thank you