the checkpout page sends the data to the confirm_cart page where it is validated. confirm_cart sends it to the confirm page where it is passed to the payment gateway from processing if you are using local checkout and have set the wizard to store in the database or send the email receipt, this will also happen on the confirm page.
eCart 6 uses form persistence to save the form data. you can return the form data using:
<?php echo(WA_getSavedFormValue('CheckoutWizard_NewFromBlank_Default','Last_Name')); ?>
where CheckoutWizard_NewFromBlank_Default is the name of the form and Last_Name is the name of the element