This feature allows you to choose custom fields that you have created on previous registration forms and copy them onto your current form. First select the Copy Existing Field button pictured below.
Once selected, the first window (pictured below) will display a list of available registrations to choose from. Pick either a Cart or Individual Level field from any of these registrations.
Once this selection is made a preview of all the custom fields from that registration will be displayed. from here select the field you want to copy as is pictured below.
Once this is done the configure field window (covered next) will appear. Here you can make any necessary modifications or keep your field as is and add it to your form.
This should help speed up building certain types of registrations.