<?php
if ( empty( $_POST ) ){
?>
<form name='registration' action='pdo1.php' method='POST'/>
  <input type="text" name="user_name">
  <input type="password" name="password">
  <input type="text" name="email">
  <button type="submit">Submit</button>
</form>
<?php
} else {
    // host, myU, myP and myDB are all correct
    $db_user = 'myU';
    $db_pass = 'myP';
    $db = new PDO( 'mysql:host=localhost;dbname=myDB', $db_user, $db_pass );

    $sql = "INSERT INTO users ( user_name, password, email ) VALUES ( :username, :password, :email )";

    $query = $db->prepare( $sql );
    $result = $query->execute( array( ':username'=>$username, ':password'=>$password, ':email'=>$email ) );

    if($result) {
        echo "Worked!";
    }
}
?>