Once you have install apache on CentOs 6.x you will need to open the port under the IPTABLES to allow incoming traffic. If you don't do this you will not be able to access the website. CentOs 6.x by default is locked down outside of SSH sitting on port 22.
Here is how to allow port *80 on your new CentOS 6.x Server.
From the terminal enter the following.
iptables -I INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT
Now we need to save the tables so that they are there permanently after a reboot.
service iptables save
to verify the tables have taken effect
now run sudo iptables -L