You need to make sure that your domain name is using your two nameservers. You can do this by using a whois command (whois example.com) or using any number of websites (eg. http://whois.domaintools.com/example.com).
Then if your domain name is using the correct nameservers, you need to configure those nameservers to return your ip address for your domain. How you do that will depend on what software the nameservers are running and what access you have to them. You need to get them returning at least an A record for your domain name pointing to your ip address (example.com IN A 10.10.10.10).
If your domain name isn't using the correct nameservers then you need to configure that at the place you registered your domain name.
Finally you'll need to configure your server to respond correctly to the domain name. This will involve setting up Apache (or whatever other web server you are running) to listen to requests for your domain. If you're only hosting one domain then you can get away with just using the default site, with your pages stored in /var/www. Otherwise you'll need to configure virtual hosts.
Then of course there's email too. Ubuntu systems have nice setup scripts for the default mail server to let you configure at least the basics. I don't know about Centos.