You need to have an registered Domain name like mydomain.com first. At the Registra, you'll have to create an A Record which resolves the domain name to your public IP (the static Server IP, public not LAN IP).
If you have an website running on that server just need to type the domain name like http://www.mydomain.com
in your browser to connect. If you've some Web Application running, use http://www.mydomain.com:
[Port No. of the Web Apps, NO bracket's]
You may have to create a proper host file on your server. On debian it would looks like:
127.0.0.1 localhost.localdomain localhost
192.168.1.100 server.mydomain.com server
# The following lines are desirable for IPv6 capable hosts
::1 localhost ip6-localhost ip6-loopback
Check with the How To for CentOS The Perfect Server ..... on this website, which may gives you all required infos.