World of "www"

OK, so now you decided to have one VPS, one IP, and many sites?
Cool, its very easy
First in the root folder, create your website folders, like you have 2 websites, so name them as site1.com and site2.com
So now you'll be having two website folders site1.com and site2.com in your root directory.

Now navigate to /etc/httpd/conf/ and start editing httpd.conf file,
At the end of the page, you will find a line, just like below

#NameVirtualHost *:80

Just uncomment that by removing # from it, So that it becomes like the below one:-

NameVirtualHost *:80

Then below their will be more lines which will be commented so uncomment them also, and make them look something like this

<VirtualHost *:80>
    ServerAdmin webmaster@dummy-host.example.com
    DocumentRoot /var/www/html/site1.com
    ServerName site1.com
    ErrorLog logs/site1-error_log
    CustomLog logs/site1-access_log common
</VirtualHost>
<VirtualHost *:80>
    ServerAdmin webmaster@dummy-host.example.com
    DocumentRoot /var/www/html/site2.com
    ServerName site2.com
    ErrorLog logs/site2-error_log
    CustomLog logs/site2-access_log common
</VirtualHost>

Thats it, after this just restart your apacheby the following command

service httpd restart

Done,
You have successfully enabled multi-site or virtual hosting on apache Centos.