Can anyone explain with some authority how the fuck the reservation system for the Auditori stage at Primavera works?

Do you have to pay €2 for every gig you want to see in there? Or is it per day? Or only certain shows, and therefore which ones? And when do they go on sale?

FSS - why the hell my ticket doesn't cover this, I do not know... if I miss Low or Owen Pallett, someone's going to feel my wrath.