In addition to the application(s) that volunteers fill out providing their references, you also need an online application that the references themselves use to respond. The instructions here assume that you're comfortable with the basics of setting up an application form in VSys Live.
Create a new application form. In its properties, Application type must be VSys Live application, Usage must be External certification update/approval via URL, Certification must be Background Reference Check. Completed date field, Log field and Posted values field can be left blank or set as below.
Place any fields you want onto the application. In most cases you'll stick with user fields, but you can also put any of your own fields from the reference check certification and read-only fields about the volunteer/applicant such as their name.
Any fields from the reference check certification itself (Add field -> Certifications -> Background reference check -> field) that you put on the application will be updated by the application when it's filled out. For example, placing the Comments field as above will put whatever the reference enters on the application into that field of the reference check itself. Putting the Result field (you'd want to limit the options available to just "Positive", "Negative" and "Neutral" to avoid them being changed to something inappropriate such as "Uncontactable" lets the reference directly recommend the volunteer. Otherwise you'll do that yourself after seeing each reference's responses.
Don't put any links to this application in VSys Live menus: this application only works when it's being used as part of a reference check.
Save the application.
Never put any private information about the volunteer on this application, or allow editing of fields that you wouldn't want edited by the reference. Anyone with access to the link in the generated letters could view and/or edit those fields!
The VSys tech support folks will happily give you a sample template to start with if you want.