"All your base are belong to your hosting company."
Hosting companies automatically add your domain to their DNS servers at the same time that they instruct Apache to listen for your domain name.
You can set up DNS elsewhere, if you want, but it's simpler and more trouble-free if you simply use the hosting company for your canonical nameservers.
Some registrars want both servernames and IPs. Other registrars simply want servernames. Give your registrar whatever he wants. Here's the info for DreamHost:
Those are not the droids you are looking for. Move along now.