POST

<?php

    if (isset($_POST['username']) && !empty($_POST['username']) &&
        isset($_POST['password']) && !empty($_POST['password']) &&
        isset($_POST['email']) && !empty($_POST['email'])
    )
{
    echo 'yes';
    unset($_POST);
}

?>
<html>
<body>

<form action="" method="post">

<p>username<br>
<input name="username" type="text" />
</p>
<p>password<br>
<input name="password" type="password"/> password should be more than 6 characters
</p>
<p>email<br>
<input name="email" type ="text" >
</p>
<p>
<input type="submit" name="submit" value="submit"/>
</p>

</form>
</body>
</html>