[CentOS] firewall and opening ports

Hi list. This is my first post here. Super newbie. I will try not to  
ask too many questions, but searching is hard when you don't even  
know where to begin. Hopefully someone can point me in the right  
direction.

I have just installed CentOS 4.2. I selected to have a firewall in  
the graphic installer, and I opened ports 22 and 80. Fine so far. SSH  
and HTTP both work. But now that everything is set up I have  
discovered I need to open port 53 in order to install djbdns.

My main question is: what did I install by choosing to have a  
firewall in the CentOS installer? Is this iptables? Or is it  
something else?

And then if anyone just wants to give me the complete answer: how do  
I open port 53?

Thanks!