1. declare a variable
2. create validation for it
   and test
   then create another
   and test
   
   $firstname = $_POST['first_name'];
     if empty($firstname) {
      echo "please include your first name";
}
then add the next variables...
create variable, create validation, test..

if ((!empty($_POST['username'])) && (!empty ($_POST['password']))) {
                if (($_POST['username'] == 'testing') && ($_POST['password'] == 'testpass')) {// username and password match