When you create a new blank form, the option Store Data in Creator will be selected by default. This means that Zoho Creator will have a table generated at the backend to store data submitted through the form. Deselecting this option will not generate a table for this form to store the data. Refer the topic, Creating Stateless Forms for more information.
The Customize Tab is used to customize the form and view layouts and themes. Refer Customize Look and Feel for more information. More customization options are provided for forms embedded into your website. Now you can customize almost all the elements like form header/footer, field width/height, label backgrounds and much more...to suit your website look. For more information, refer Customizing look & feel of embedded forms.
To view the script definition of a form,
The script definition of the selected Form will be displayed in the Script Tab. If you are well versed in deluge scripting, you can modify your application by making the required changes to the script definition. The changes made in the script will be reflected in the GUI.