The error is occurring because the code for server validation is missing from the head.
add the following at line 1:
<?php require_once("WA_ValidationToolkit/WAVT_Scripts_PHP.php"); ?>
<?php require_once("WA_ValidationToolkit/WAVT_ValidatedForm_PHP.php"); ?>
the development process is dependent on what you wish to accomplish with the page, you would only need to use DataAssist if you wanted to store the form data in a database.
if you only wish to email the form, you just need to apply universal email after creating the form with CSS Form builder.
the settings to use for the email server depend on your host. Your host should be able to suplly you wit hthe correct SMTP server to use.