Actually, you don't even need to go to the desk anymore. You walk to the DME area at the airport and show your voucher to someone with a hand-held scanner. They scan your voucher and show you to the bus queue area.
It is accurate that you can arrive with zero paperwork and still ride the bus. In this case, you'd have to go to the DME counter and show photo ID (one person per party) and they'll print you up a new voucher.
When you receive your DME mailing, there will be instructions in the booklet.
The most important thing to do is make sure you have a DME reservation. DME is free but it isn't automatic ... you have to opt-in.