Very basic DNS question.

I have a small network (10 pc’s) that previously had no internet/email access.

I have just installed a DSL router and a firewall.

I’ve been told that the PC’s DNS address should be an internal address, so how will I be able to get out on the internet?

Do I need to set up DNS on a server, or can I set this up on the firewall or router?

Any help would be greatly appreciated.