Adding custom fields to a checkout form
Creating a custom field on your purchase receipt for the purposes of getting more information from your customer - i.e. their preferred T-shirt color, their shipping address, or their A/S/L - is easy!
First go to your product's Preview page and look to the left side of the page.
Underneath the dropdown Payment Form, type over "Enter Placeholder" the message you want your customers to answer, and click the box to require that box to be filled out before purchasing.
If you simply want to require your customers to enter shipping information, you can tick the box Require Shipping Information.
Click Update to save changes. To delete a custom field, simply highlight the text and hit backspace on your keypad.