dkp is what's spent to get endgame epics.
you get pts for raiding with your guild and you can then spend them however you choose.
various guilds use various methods of dkp spending.
for instance, my guild use to set a standard dkp worth on all items and when that item drops, everyone on that particular raid who wanted the item would whisper our master looter. all of their dkp were brought up on an ingame list and whoever had the highest dkp got it by default for the set amount.
now it's a bid system, minimum of 5, increments of 2. so everyone who wants it whispers, list is generated, bidding starts. bidding ends when there is one person left bidding.
grats on 40.