Adding custom fields to the registration form
In order to add fields to the registration form, custom fields must be added to the primary group. The primary fields group is the group that is created by default when WPUM is first activated and cannot be deleted. You will also notice a message on top of the table telling you that this is the primary group and fields added to this group can be displayed into the registration form.
Once you have created a field, you'll be redirected to it's editing page. When editing a field into the primary group, a new setting will appear on the right side of the screen where you can select whether or not to display this field into the registration form.
Enable the option and save the field.