After purchasing the voucher, you make your reservation on the AREX website. It's easy once you get used to it, and you can even change the train time you've already booked on the website. At the ticket gate, a railway official told me that even if I purchased tickets for multiple people, I could just scan the voucher of the person who made the reservation. (They said that the tickets were linked, but it wasn't clear if there were more than two people; up to two people were able to pass through.) The seats were spacious and very comfortable.