Add fields to the registration form
Certain fields can be displayed into the registration form. Not all fields can be changed, and specific fields (e.g email) will always display.
The "Primary" fields group is the only group that can display fields into the registration form.
In order to display a field into the registration form, click the "edit field" button of the field you wish to customize.
You will be redirected to a new page where you can customize the field.
On the right side of your screen you will see the "Show on registration form" box.
Click on the "Display this field on registration ?"
Once you have finished, click the "save field" button, to save your changes.