If you have your hosting and your domain purchase from the same company you probably will not have to worry about this. Many times your domains are purchased at one site, your registrar, and your host of your servers is at a different site or with a different company. This is simple to correct … it is a matter of pointing the nameservers to the hosting site. An example would be that your purchase your domains from Namecheap and your servers are hosted with A2 Hosting.
What you will want to do first is login to the site where you purchased your domain from, registrar. Within the site somewhere, you will be able to manage the domains … the video in this post uses Namecheap as an example. You are looking for the section called nameservers. You should be able to add nameservers that are provided to you by your hosting company.
… custom DNS settings … eg xxx.domain.com … sometimes they come with an xx1 and a xx2 … the two will look very similar so be sure to add in the appropriate area a unique DNS entry.
Propagation Of Your DNS Entries
Once the nameserver entries are saved with your registrar, place where you purchased the domain, the site will begin to propagate. When you update the nameservers for a domain, it may take up to 24-48 hours for the change to take effect. This period is called DNS propagation. In other words, it is a period of time ISP (Internet service provider) nodes across the world take to update their caches with the new DNS information of your domain.
Propagation can be checked a various places but I have found this site to be useful: WhatsMyDNS.net.
In most cases the propagation starts immediately and with about 30 minutes you will see the propagation start to occur. I realize the hosting sites say wait 24 to 48 hours, but if entries are not updating within 30 minutes you probably have done something incorrectly. Do not wait the 24 hour time frame if you are having issues with any movement in propagation. If you are unsure call your hosting site and get a tech on the phone to do some checking.