What do you need/use DNS service for?
The DNS server is the internet server that provides an IP address for a domain. It keeps a registered list of IP addresses (machines) which are "authoritative" for that domain.
So if I'm running a webserver for my site "widgetables.com" on a machine that has the IP addy "44.55.66.77" then I need a DNS server to tell the world that anyone looking for widgetables.com really needs to be pointed to 44.55.66.77.
Same for mail, ftp, sub-domains etc etc
When you type in widgetables.com in your browser, the first thing the browser does is query the DNS server for the IP address so it knows where to fetch the pages from.
TJ
If you bought yourself a shared or dedicated hosting server and buy your own domains elsewhere (in other words you shop around rather than do everything with a one-stop shop) then you will need DNS services from somewhere to point one at the other. If you see what I mean...
A lot of domain suppliers offer control panel type services so that you can buy a domain and just login and point the DNS to wherever you want. 123-reg do just that.
OddDog is obviously bulk buying through someone that offers no such services, so he'll need to transfer the domains elsehere in order to point the domains somewhere useful.
TJ