A form field is only required if you set it to be required in the server validation server behavior.
The server validation server behavior is where you control what form fields are required and which are not.
to add a new form filed to the registration page, place your cursor where the new field should be added, then go to Insert -> Form -> Text Field to add a new text field, in the box that comes up, give the text filed a name and ID.
After adding the new form element, you will need to edit the insert record behavior. go to Window -> Server behaviors to open the server behaviors list and double click the insert record behavior.
you will need to select a database column, click the lightning bolt next to value and select the new text field to have the information entered in the form stored in the database.