I nees some more help

I don't understand german and never had bought anything on Net. so can someone help me.
I'm planing on going to Vienna concert, here is the web site from where I would like to order tickets.
http://www.oeticket.com/scripts/det....00000000000000

click on Ticket info, and there in new windw down on Sitzplatz. I don't understand what does kat. 2 (in red)mean? Is it all those red places in stadium, or some particular like Rang 2,sector a, or rang 3,sector B?
I would like the tickets for 2.Rang sector A or C. But there when I fill what ticket I want it says only kat.2. Will I make mistake, coz I don't want the tickets for sector B? Does it mean that I'll have to come early enought to be in sector C or A?Please help me I have never been on BJ concert and this is my first one

I guess the tickets that you want (Sektor A or C) are sold out and it only shows up the tickets that are still avaiable.