If you would like to add a custom fields to a page or email by doing the following.

Example: I wish to ask people how they came to the website in the billing page. 

1. Log in to Joomla Administrator
2. Click on Seber Cart->Configuration->Customer Details
3. Scroll down to Misc 1 and enable the field
4. Click on Seber Cart->Configuration->Language Editor
5. Select the page you wish to have the field on example "Page: Billing" find misc 1 and change it to "How did you here about us?"
6. Click on the save button
7. Open the Language Editor again and find "Email Order: Notification" making sure that !!CUSTOMER_MISC1!! is in the email, this will show what ever the customer entered in the field on the email and in orders.