I've been on the reserve list for like 3 years now, I was sent an email before the last season saying i can book tickets but it will be pure luck whether I get picked to go. I wasnt lucky enough but I've just got another email recently for the new series basically saying the same thing.
You get asked to pick a date, and how many tickets you want then you get put on another list where x ammount of people will be picked to actually go and see them
I would check with your friend to find out if he's actually been picked to go, or whether he's just been given the chance to "reserve" tickets on the off chance he gets picked