a few questions abotu DNS

alright, i'm about to buy a dedicated server but and confused on a few things about domains and stuff. First off, when i went to ask the guys a question they said i had to buy a domain and put it on their name server, my question is, why can't i put the domian in my sever than i'm abotu to buy? And that leads me to my next question, when you buy the server and buy domains to host on it, can you host the domains on that server or do you have to have it on antother server? Thanks for anyones help;

the www works like this:
- there is name servers. a whole network of name servers. they know which names resolve to which ip.
- there is www servers. they listen on ip addresses.
- then there is the clients (browsers). they ask the dns servers to whom (which ip) the domain belongs, then they connect to this ip.
- the client can ask any dns server, if the server does not know the domain, it´ll ask another server for it. it will also cache the answer then.

conclusion:
- you can leave your provider with all the trouble of configuring and running a nameserver and only tell him which ip you have. you still have all other freedom to configure your server.
- because of most nameservers caching other nameservers´ responses, it can take up to 48 hrs after you changed your domain until every server knows about it.
- you probably don´t want to run a dns server since it would probably take you months for learning and setup. and it´s IMHO really not worth the effort unless your provider charges more than $10 for changing the nameserver tables and you want to change quite often (maybe you have several IPs and experiment with load balancing or whatever)

our company´s provider (germany) charges nothing as long as we don´t want to change every week. But also we have 15 domains hosted on his servers already, so he really SHOULD not charge for minor stuff like that