Domain Name pointing to another hosting company

1) Make sure the domain is registered and is pointed to your nameservers, if you're managing the DNs

2) In order for the site to work, the other host has to have the domain set up in their webserver config

 

Just to add to what Vanessa said...

You're partway there. Your cname will redirect people who are trying to hit the domain to the existing server, but all that does is tell them that IP address for 'domain b' is the same as 'domain a', which is fine...

... until people arrive at the IP address for 'domain a' and the user's browser says "hey, I'm looking for 'domain b' " at which point the webserver says "I have no idea who you're talking about"... they'll have to change stuff on their end.

Having said that, there ARE things like 'custom DNS' at dyndns.com that will handle all that for you, as it basically rewrites some things from the end-user's perspective. However, what it does *not* do is make 'domain a' appear to be 'domain b'... which means that they'll get where they need to be, but they might wonder "how did I get here? I wanted to be at 'domain b' !"