WoTLK Death Knight spec??

So i'm gonna ask a very noobish question that's been bugging me for a while..

I didn't play WoW for years.. and now i started and made a Death Knight, but i didn't get to choose blood/frost/unholy specialization..
Can someone explain to me when do i get the chance to choose one? at start? later ingame? or never? under what circumstances? I get and I'm able to use talent points on all 3 of them in talent(n) bar, but i can never choose which spec. I am.. or does dk work without making a choice?

in WoTLK you don't choose a spec as you do in later expansions, you just put your talent points into whichever tree you want to go with.