Before you add a new Volunteer to your Roster, you should ask them to register with the Applicant Gateway, which collects their Social Security Number, contact info, and "bio-demo" identifying data.
You can send them a direct link to this page to get started:
Once they have registered with Applicant Gateway, you can add the volunteer to your roster by following the instructions in Adding A Volunteer With A Go Pass To Your Roster.
Note that it is possible to add a new Volunteer to your Roster before they register with Applicant Gateway, but you will need to fill in their full suite of contact information and date of birth to proceed. By having the volunteer register with Applicant Gateway first, this information will already be filled in.